It should surprise no one that atheists often don’t get along. I have come to believe it has very little to do with atheism providing no cohesion, and more to do with the type of person who becomes an atheist.
Atheists are people able to look around at those we love, who are like us, who we care for and who care for us, and be able to confidently say to them, “You’re wrong, and I’m also pretty sure you’re a moron.” Atheists criticize not because they don’t care about others peoples’ feelings, but because we care about others as human beings capable of overcoming superstition, and we don’t want people we care about to be so willfully ignorant. Many atheists are incapable of shutting up, and this is something I hope never changes. It may be the one redeeming quality of atheists.
A good atheist is not measured by silence or obedience, but by being able to take endless criticism, and not only the attacks which one might expect to come from the religious, but also in the form of barbs from fellow atheists. Atheism is not for the weak willed or those who shy away from confrontation. For these types of people, I recommend Buddhism.