I was curious, if an atheist friend of yours showed interest in becoming religious or joining a church... what would you do? Would you try to dissuade him or her? Would you be supportive?
I know many religious people who try to dissuade people they know from becoming an atheists, so I am just wondering if it works the other way around?
No, I wouldn't stop him. People are free to believe what they want. There is freedom of Religion but also freedom from Religion, although the latter one is often ignored. I would, however ask him why and what his reasons are and explain to him what my subjective opinion of religion is. Maybe I want to achieve that he doesn't convert, but actually I shouldn't. If he is rational he wouldn't convert to religion I think.
Because religious people are trying to convert others and stop people from becoming atheists, it would be unwise to use that method as well. In doing so, we would actually support religion. People who are really true believers can't tolerant I think because every religion claims to be the absolute truth.
I would at very least ask them to examine the decision closely and talk at length with them about why they made the choice. If during the conversation that it becomes apparent that this person has made up thier mind to follow God then I would seriously question their atheism but would leave it there and live with their decision.