Well there are gods and there are gods, aren't there? I mean, a Christian, a Muslim and a Sikh all agree that something they call 'God' exists, but beyond that, opinions as to who or what He really is diverge wildly. Hell, you don't even have to go outside a single religion to find big disagreements about the nature of God and how He wants us to live - look at Catholics/Protestants, Sunnis/Shi'ites, Mahayana/Theraveda...whereas there's never going to be a violent schism between rival sects of atheists.
Yeah, it's not as simple as atheists vs. believers. In some sense, atheists have more in common with believers than believers do with each other. Believers are also non-believers. The Christian doesn't believe in all gods but one: her/his own. Likewise for the Jew, the Zoroastrian, the Muslim, the Hindu, the Druze, etc, etc.