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?
I would ask them to find out what claims & doctrines that church espoused before even touching it, then see what the objections and evidence against those individual claims modern scholars and scientists offered. If need be, I would ask them about specific beliefs: "Do they believe that 8 people aboard an ark managed 2 or 7 of every kind of animal on the planet, that a global flood wiped out the rest of life, and that the 8 people and 2-7 of every kind of animal repopulated the entire earth? Do they believe the Noah's ark story is true?" After finding one, I would make a comprehensive argument as to the wrongness of that claim. I would find examples of preachers/apologists blatantly lying about the said topic and show it to the friend.
If the friend was resistant to being deterred by facts, I would find out what about joining (that )religion appealed to them, and try to demonstrate that said religion is not ideal or even necessary for that purpose.
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.