Since it is grammatically correct to spell God as God, then why do some spell God as god, with lower case?

Spelling god with a lower case g isn't really being intolerant toward religion. Its just saying I personally don't believe in it so there is no need for me to capitalize it because it holds no real significance in my life. That is a far cry from being religiously intolerant. If god is so important to you then you are can capitalize it doesn't mean to me what it means to you. Also, who says the only grammatically correct way to say it is with a capital? When I type god it does not get the little red squiggly line under it. To me, its just a preference thing. I do the same thing when talking about braille. Allegedly its supposed to be capitalized but intentionally lower case it because I'm not talking about the guy who created the system, I'm talking about bumps on a page. Same thing to me.