Contraception can't protect you because it does not cover your heart.
Sin always harms you: spiritually, intellectually, in your social capacity and creativity, emotionally and, yes, physically too.
Condoms do not protect the heart, nor do they address the heart of the matter, which is sin. That is why contraception is bad. It doesn't deal with the problem, just the symptoms. Using a condom is like putting a band-aid on gangrene. Cut out the gangrene and the band-aid is not necessary.
The goal is not simply external cleanliness. We are not pharisees or puritans. We believe in the heart. We believe in the human person. We believe in Jesus Christ who said that it's not about keeping the outside of the cup clean but rather the inside! "Thou blind Pharisee! clean first the inside of the cup and of the dish, that the outside too may be clean." Mt. 23:26
The problem is being good and not just looking good.
For...beauty passes and virtue remains.