Religion is striving for an ideal. Nobody is perfect.
I'm going to guess that the condemnation is firstly addressed at themselves. They have to condemn the act so they won't begin to feel it's ok. Maybe it's an obsession, like "for the next 30 seconds, think about anything except peanut butter"--you'll think about peanut butter to make sure you don't forget what you're not supposed to think about and think about it by accident. whew! It's a sin, and they're committing it, and they want to keep it hidden, so they focus on it.
