How can someone really be an atheist if they hate a God that they claim does not exist? Nobody hates Santa Claus or the Tooth Fairy.
Atheists tend to fall into several groups. Some don't believe in God but they have no hostility towards anyone who believes in anything.
Another group of atheists are those who hate God because they don't like how He runs his universe. Or because they know that God hates their sin and they love their sin.
Others are fools that act superior because they don't believe in God. Actually, among atheists, I prefer the arrogant, hateful, and condescending atheists because they make themselves and their beliefs unattractive.
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.