The evil in the world is obvious and upsetting. Atheists, no less than others and perhaps even more so, are exercised by creation's terrors. Earthquakes and tsunamis kill thousands, diseases terrorize, floods destroy and droughts starve. Then there is the seemingly unending narrative of predation in the biological world. Nature is red in tooth and claw, as Lord Tennyson put it.
Atheists often proclaim this problem of evil as a justification for their beliefs but ironically this evil is as much a problem for atheism as it is a motivation. The problem is that atheism fails to explain the existence of evil.
Atheists say that we are able to identify evil as evil because the knowledge of what is evil evolved in our brains. But if that is true then there is no such thing as objective evil. Instead, evil is subjective. We may generally agree that something is evil, but that is only because of similar molecular interactions in our brains that happened to evolve, not because that thing is itself evil. There is no immaterial, objective standard which defines evil-ness.
One might think that atheists could agree with all this, but it is not so simple. Atheists could dispose of objective evil, but then they lose their raison d' etre. God is no longer responsible for creating or allowing evil because there is no such thing as true, objective evil. It is all just in our heads.
In fact, atheists very much do believe there is an objective standard. And they very much hold God to that standard. As PZ Myers wrote:
We go right to the central issue of whether there is a god or not. We're pretty certain that if there were an all-powerful being pulling the strings and shaping history for the benefit of human beings, the universe would look rather different than it does.
This is religion and it is the driving issue. It is no different than what David Hume and thousands of other atheists have been saying for centuries. God wouldn't do it that way and so our only option is atheism. This is what animates atheists. They cannot then turn around and drop their weapon, as though they never used it.