It is utterly important, when preaching (or defending) the faith, to do so in charity, as St. Paul and St. Peter commanded us:
"Speaking the truth in love, we are to grow up in every way into him who is the head, into Christ." (Ephesians 4:15)
"Always be prepared to make a defense to any one who calls you to account for the hope that is in you, yet do it with gentleness and reverence." (1 Peter 3:15)
This excellent article explains why: Airline Apologetics.