If someone hates gays on the idea of it being sin, then you're absolutely right, not related to being a bigot. That being said, I don't think most people do. Since most of the people who will talk about 'hateing gays' will be lusting after the hot girl in the bar or in the mall. And if they hate the sin of homosexuality, they should hate the sin of lusting.

Like Biggin said to most people the hate of homosexuality is a lot closer to being a bigot. They don't like them because they are 'different'.