Atheism implies belief in: empiricism, naturalism, evolution and humanism.
It might do to you, that may be why you consider it a religion. It doesn't to me. Just because people who don't believe in a god are more likely to believe some other things than religious people, does not make it a religion. If short people were more likely than others to believe some things, does that make being short a religion?
No one can know that there's no god absolutely. That being said, no one can know anything absolutely (with the possible exception of cogito ergo sum, but that is problematic too). The brain in a jar argument isn't very useful.
All that being said, I believe there is no god. However, this is an entirely pointless question, in my opinion, and doesn't affect my life in any way whatsoever. What affects my life is my lack of belief in some of the more popular gods, and that's what makes me an atheist.
Back on topic, I'm from the UK, and we have a law outlawing incitement to religious hatred. Now I do hate some religions (Scientology, fundamental Christianity, some Islamic sects), and I would encourage others to hate them too.
See what I did there? I just broke the law. Chances of me getting charged with a crime = 0%. Yeah, well I didn't really :
29JProtection of freedom of expression
Nothing in this Part shall be read or given effect in a way which prohibits or restricts discussion, criticism or expressions of antipathy, dislike, ridicule, insult or abuse of particular religions or the beliefs or practices of their adherents, or of any other belief system or the beliefs or practices of its adherents, or proselytising or urging adherents of a different religion or belief system to cease practising their religion or belief system.
It specifically allows abuse of religions. The incitement to religious hatred law is actually actually pretty specific : "A person who uses threatening words or behaviour, or displays any written material which is threatening, is guilty of an offence if he intends thereby to stir up religious hatred."
Key word : "Threatening". It seems pretty sensible, but the trouble with this, and a whole host of laws that Labour introduced under Tony Blair, is that it was already illegal. They also criminalised setting off nuclear devices in towns and cities. Because that wasn't illegal before, right?