Adoration of the Blessed Sacrament is a long tradition in the Church, at least in the Roman Rite. Although it did not always exist in the form we know of it today, St. Augustine wrote that the Eucharist can not properly received if it is not first adored (Exposition on Psalm 98, n. 8):
And because He walked here in very flesh, and gave that very flesh to us to eat for our salvation; and no one eateth that flesh, unless he hath first worshipped: we have found out in what sense such a footstool of our Lord’s may be worshipped, and not only that we sin not in worshipping it, but that we sin in not worshipping.While the manner of this worship and adoration has changed throughout the centuries, the Church has always promoted it as proper: the Blessed Sacrament is, after all, the Precious Body, Blood, Soul, and Divinity of our Lord Jesus Christ. Because it is Jesus Christ, whole and entire, under the appearance of bread and wine, it is completely appropriate to render unto It the same worship and adoration due to God Himself. In the Eucharist we recognize by faith the Real Presence of the God of the universe. Vatican II said nothing to the contrary, of course. (How could it?!) There is nothing in the documents of Vatican II that disparages, discourages, or otherwise speaks against Eucharistic Adoration.
So why do some people in the Church speak against it? To know why, we must first know what they say.
The first quote is from Fr. Richard Vosko, known for his "wreckovations" which are based on Environment and Art in Catholic Worship (and supposedly on the documents of Vatican II themselves).
"One reason why our churches are so susceptible to crime is because they are empty during the week. Maybe people who have organized vigils before the sacrament — that’s a wonderful practice to keep vigil — to take turns keeping vigil over the Blessed Sacrament that is primarily saved to take to the sick and dying — that is what the Church teaches us. I think that’s a wonderful practice, to take turns keeping watch, just in case your mother or father needs Holy Communion on their death bed. Wouldn’t it be nice to know that you can go to the tabernacle and find the Body of Christ in it?"Fr. Vosko is reducing Eucharistic Adoration to "keeping vigil" to make sure the tabernacle stays safe, so that we can be sure that there will be Hosts available in case of emergency.
Now, there's nothing wrong with making sure the Eucharist is reserved for emergencies... I mean, when we adore Christ in the tabernacle, we're not adoring the tabernacle, but what is inside it. We know he is present (that there is in fact the Blessed Sacrament inside) because of the lamp burning nearby.
However, we are not merely keeping tabs on the tabernacle. We are there to adore Jesus Christ in the Eucharist. When the Host is enthroned in a monstrance and placed upon the altar, we aren't guarding the tabernacle, we're worshiping the Blessed Sacrament exposed on the altar. Fr. Vosko seems to reduce "adoration" to "keeping vigil" (and not in the Gethsemane sense).
The Church says, in Eucharistiae Sacramentum, n. 5, that "[t]he primary and original reason for reservation of the Eucharist outside Mass is the administration of viaticum. The secondary ends are the giving of communion and the adoration of our Lord Jesus Christ present in the sacrament. The reservation of the sacrament for the sick led to the praiseworthy practice of adoring this heavenly food that is reserved in churches. This cult of adoration has a sound and firm foundation, especially since faith in the real presence of the Lord has as its natural consequence the outward, public manifestation of that belief." But just because Adoration was not the original reason for the reservation of the Blessed Sacrament does not mean it is a disposable reason.
An article from America magazine says that one sentiment during the late 1960's was that "[t]he purpose of the eucharistic species, then, [was] not to be the object of adoration, but the daily food of God’s 'pilgrim people.'" If only it was the daily food! (But I'm not one to talk... I haven't regularly attended daily Mass since Easter of 2007...) But this again echoes the misconception that Vatican II put away the notion of the Eucharist as fit for adoration.
This concept of the Eucharist as (merely) an "object" also came up in two homilies (given last year and this year, on the feast of Corpus Christi) from the pastor of a parish in Illinois (which happens to have a Perpetual Adoration chapel):
"For many folks, the Eucharist was an object, a holy thing that you put in a gold container, and you kept your distance from the Eucharist. Oh, you had great reverence and respect as I said, but many people felt very unworthy of the Eucharist. So the Eucharist was an object, a holy thing, looked at and observed..."I'm curious what, exactly, this priest believes Vatican II "tried to change". Rood screens were already out of fashion for some time, ocular reception was handled before then (and Pope St. Pius X encouraged frequent reception of Holy Communion), and the Council certainly didn't speak out against Adoration. I'm not fond of the language used in the more recent homily: the pastor never mentioned adoration among the things to during the time of Eucharistic devotion, but describes it instead as "tak[ing] time out for an hour" (focusing on what it does for you instead of what it does for God, that is, render glory unto Him), and he uses the phrase "present in a pre-consecrated to blessed piece of bread" which I consider painfully vague.
"Right behind that wall where I'm pointing is the Sacred Heart chapel, and for years now we've had people doing Eucharistic Adoration 24 hours a day, 7 days a week. We are inviting you this weekend, if you feel so moved, to make a commitment to that kind of praying. Now I want to be clear about something. When we started Eucharistic Adoration some people got angry because they said 'you're treating the Eucharistic like an object, like a holy thing'. In the Middle Ages that became such a prevalent mindset -- the Eucharistic as a holy thing -- people stopped going to the Eucharistic, they just looked at the Eucharistic in a monstrance. Colin and Jim ... were reviewing some history for us: they used to have screens in front of the sanctuary, and sometimes the congregation would yell out 'hold it up higher!' so that the Host could be seen by people who were screened out. And Jim mentioned 'ocular' reception of Communion; that's how most people, many people in the Middles Ages received Communion: ocular reception, looking at it. Vatican II has tried to change all that. The value of Eucharistic devotion is in this busy, noisy world, to take time out for an hour, to be still, to be prayerful, to meditate, to contemplate in the presence of Jesus Christ present in a pre-consecrated or blessed piece of bread."
The Real Presence web site offers a few objections that are frequently heard: it "is too private, too personal, or even too quiet"; or it takes too much time, and "wouldn't it be better to spend that time, say, visiting the sick?"; it is "too much 'Jesus and I' [and] tends to be selfish"; and, of course, that somehow private devotions (including adoration) "are discouraged and even forbidden by Vatican II". Each of these objections is refuted on that web site, so I encourage you to read the page I've linked to.
So now that I've provided numerous examples, what is my take on why people are discouraging Adoration? I have three possible reasons.
First, the misconception that the Church Herself actually discourages Adoration since Vatican II. This erroneous thinking places Adoration in the "pre-Vatican II" category, along with everything else old and medieval and backwards. But this conclusion is patently false; several documents from Popes and particular Congregations of the Roman Curia have spoken about it and provided regulations for it. Popes John Paul II and Benedict XVI have praised and promoted Eucharistic Adoration, and lamented its decline and virtual absence following Vatican II:
"Adoration of Christ in this sacrament of love must also find expression in various forms of eucharistic devotion: personal prayer before the Blessed Sacrament, Hours of Adoration, periods of exposition - short, prolonged and annual (Forty Hours) - eucharistic benediction, eucharistic processions, eucharistic congresses." (1980 - Pope John Paul II, Dominicae Cenae, n. 3)Second, in over-emphasizing the Eucharist as a meal and under-emphasizing it as the Holy Sacrifice, the thought of reserving a Host for exposition and adoration seems silly. Why look at it when you could eat it? What good does the Eucharist do if we're not receiving (or taking) it and eating it? It becomes "an object" rather than "the object [recipient] of worship". I wonder if "spiritual communion" is at all preached in the parishes where the Eucharist is seen as a communal meal.
"After the Mass of the Lord’s Supper, the faithful should be encouraged to spend a suitable period of time during the night in the church in adoration before the Blessed Sacrament that has been solemnly reserved." (1988 - Paschale Solemnitatis, n. 56)
"There is a particular need to cultivate a lively awareness of Christ's real presence, both in the celebration of Mass and in the worship of the Eucharist outside Mass. ... During this year Eucharistic adoration outside Mass should become a particular commitment for individual parish and religious communities." (2004 - Pope John Paul II, Mane Nobiscum Domine, n. 18)
"Indeed, in our age, marked by haste even in one's personal relationship with God, catechesis should reacquaint the Christian people with the whole of Eucharistic worship, which cannot be reduced to participation in Holy Mass and to Communion with the proper dispositions, but also includes frequent adoration - personal and communal - of the Blessed Sacrament, and the loving concern that the tabernacle - in which the Eucharist is kept - be placed on an altar or in a part of the church that is clearly visible, truly noble and duly adorned, so that it is a centre of attraction for every heart in love with Christ." (1999 - Responsum ad Dubium on Contempt for the Eucharist, n. 2)
"In many places, adoration of the Blessed Sacrament is also an important daily practice and becomes an inexhaustible source of holiness. The devout participation of the faithful in the Eucharistic procession on the Solemnity of the Body and Blood of Christ is a grace from the Lord which yearly brings joy to those who take part in it. Other positive signs of Eucharistic faith and love might also be mentioned. Unfortunately, alongside these lights, there are also shadows. In some places the practice of Eucharistic adoration has been almost completely abandoned." (2003 - Pope John Paul II, Ecclesia de Eucharistia, n. 10)
"It is the responsibility of Pastors to encourage, also by their personal witness, the practice of Eucharistic adoration, and exposition of the Blessed Sacrament in particular, as well as prayer of adoration before Christ present under the Eucharistic species." (2003 - Pope John Paul II, Ecclesia de Eucharistia, n. 25)
"In the Most Holy Eucharist, Mother Church with steadfast faith acknowledges the Sacrament of redemption, joyfully takes it to herself, celebrates it and reveres it in adoration..." (2004 - Redemptionis Sacramentum, n. 1)
"Therefore both public and private devotion to the Most Holy Eucharist even outside Mass should be vigorously promoted, for by means of it the faithful give adoration to Christ, truly and really present, the 'High Priest of the good things to come' and Redeemer of the whole world." (2004 - Redemptionis Sacramentum, n. 134)
"It is moving for me to see how everywhere in the Church the joy of Eucharistic adoration is reawakening and being fruitful. In the period of liturgical reform, Mass and adoration outside it were often seen as in opposition to one another: it was thought that the Eucharistic Bread had not been given to us to be contemplated, but to be eaten, as a widespread objection claimed at that time." (2005 - Pope Benedict XVI, Address to Roman Curia, n. 30)
"A growing appreciation of this significant aspect of the Church's faith has been an important part of our experience in the years following the liturgical renewal desired by the Second Vatican Council. During the early phases of the reform, the inherent relationship between Mass and adoration of the Blessed Sacrament was not always perceived with sufficient clarity. For example, an objection that was widespread at the time argued that the eucharistic bread was given to us not to be looked at, but to be eaten. ... With the Synod Assembly, therefore, I heartily recommend to the Church's pastors and to the People of God the practice of eucharistic adoration, both individually and in community." (2007 - Pope Benedict XVI, Sacramentum Caritatis, nn. 66-67)
Third, and hopefully not true, it is an attack on the Real Presence. This flows somewhat from the previous reason: if we see the Eucharist primarily as a spiritual meal and ignore that it exists as efficacious food for us only because it is first the Holy and Perfect Sacrifice of Jesus Christ, then we run the risk of losing the understanding of the Real Presence. Offering bread and wine to God in propitiation for our sins is utterly useless; the only reason the Sacrifice of the Mass is worth anything is because it is worth everything, because it is the self-same sacrifice of Jesus Christ: his Body, Blood, Soul, and Divinity, present under the forms of bread and wine. But if you stop seeing the Eucharist as a sacrifice, then Jesus doesn't need to be really present in it, he can be simply "spiritually" (whatever that means) present in it, present only in a subjective way, not a doctrinally defined way. Once you've done that, to worship the "Eucharist" would be to worship a piece of bread, and that would be idolatry (although idolatry is becoming less and less noticeable nowadays).