Christ loved the Church and gave himself for her so that she would be 'without stain.' And the Church would be without stain if we were not a part of it! The Church would have one less wrinkle if I committed one less sin. Martin Luther criticized Erasmus of Rotterdam for remaining in the Catholic Church despite its corruption, but Erasmus answered him: 'I put up with this Church, in the hope that one day it will become better, just as it is constrained to put up with me in the hope that one day I will become better.'
(H/T: Fr. Jay @ Young Fogeys)