We have had a few god-believers who stick around for quite a long time. Most have been relatively reasonable and fun to interact with. After a while, they understand that we don't accept statements from religious scriptures as truth unless there is a factual basis. They realize that nobody here is going to accept bogus arguments about why their god does not seem to exist. They generally get worn out and leave on their own. They are welcome back anytime.
I can think of three off the top of my head who were truly awful people: insulting to everyone, giving out smites to anyone who disagreed with them, linking to crazy websites instead of answering questions, refusing to engage in a sensible manner, and being a general pain in the a$$. We tolerate them for far longer than most religious sites tolerate atheists (where anyone who asks too many questions gets banned). After several attempts to get them to behave and play nice, they end up banned.
I don't think belief has anything to do with it--some religious people are nice and others are just jerks. But religious jerks think they are better than we are, no matter how badly they behave. Because god.