GL, I think it would depend on the context and how they say it. You could certainly talk about your spiritual feelings and what atheism means to you. It would be invalidating for anyone to come in to your thread and say that you are wrong for believing as you do. I don't see the point in coming to a thread about atheism and saying "I believe in God." Hypothetically, was there a request for everyone to contribute what they believe or don't believe, or is it just out of the blue? I think we would have to know the context - It would certainly be inappropriate if they said that there is something wrong with you for not believing in God, or that you can't be spiritual, or anything that invalidates your feelings and beliefs.

One difference is that "I believe in God" is stated positively and is about that person's beliefs. It doesn't change what you believe, or suggest anything against what you believe. Something like "I don't accept that atheists can be spiritual" would contradict your statement of your beliefs, and that would be inappropriate.

Does that make sense?