Theism has its times of doubting, most certainly, but it also has a line of policies and beliefs that it almost invariably promotes. Many forms of theism discourage straying too far from dogma. Atheism, however, gives you this flexibility. Atheism, maybe more than any other religious belief, potentially allows you the most freedom to change your mind. We all change our minds, sometimes not just in small ways, but in gargantuan ways.
People convert to other religions, and sometimes to completely different ones.
It's hard to say, but many show disfavor to say the least. As an atheist, the moral world is yours to explore and decide upon. If my atheist friend decides that Christianity would be better for her personally, I would wish her well. Just because I do not prefer Christianity doesn't mean my friends shouldn't either, after all. I would hope this endeavor would be relatively reflective and intelligent, but I can only hope.