I had a friend (coworker) who was insanely religious. Brought his bible to his cubicle everyday, highlighter markings, sticky notes all over it. I would always argue with him about it (I was 18-20 at the time and hadn't gotten fed up with doing that yet) and try to explain evolution and natural selection to him. It never got anywhere, so I thought.

I left that job and stayed friends with him (wild, you can be friends with people you disagree with!). About 4 years later he messaged me on Facebook (I had move states) and told me he's become an atheist. He spent a lot of time trying to rationalize his beliefs and realized he was just lying to himself. And that our conversations helped bring that about.

So, I guess that's why you bother.