There are no atheists who 'hate' God. You cannot hate something that you don't believe exists. So in fact, they can't be atheists if they hate God. You can only be an atheist if you don't believe God EXISTS. Like, at all.
You're probably used to the line of thinking that God does exist, and can't comprehend God not existing. The logical choice then would be to think that atheists hate God.

Nobody stops believing in God because they 'want to sin'. A lot of atheists are against the religious' preaching against sin. When you don't believe in Allah (and aren't vegetarian/vegan) there's no reason not to eat pork. It's the same for us with sin. Why would we not have as much fun as we possibly could in life, whilst it hurts none? The religious aren't hurt by our sin at all, but act like they are nonetheless.

Furthermore, we don't believe in sin. This means: there is nobody 'up there', so nobody is hurt by us having sex before marriage.