Most people do not come to a conclusion based on careful consideration of evidence and detached examination of the world around them. Most decisions are made based on emotion and influence of peers. A choice for atheism does not necessitate some higher learning or cognition any more than a choice of religion automatically bespeaks enlightenment. Few people following a religious belief arm themselves with a true understanding of their religion, just as few atheists likewise arm themselves with a true understanding of their ideology. More often than not the atheists I have encountered are simply angry at someone and want attention. There are those that truly believe in no God, which is well and good. Still, being an atheist does not automatically grant rational thought and an understanding of the skeptic.
You're right; in the heat of the moment and when emotions are running high, we do default to emotion. You've had a bad day. Your pet is ill, you hurt your leg and lost your wallet. First thing you think is 'Ugh, what have I done to deserve this? Fuck sake!'. However, a rational person goes home and after a bath and some chocolate simply accept that today was a day where a lot of things went wrong, you'll phone the vet in the morning, your leg will be better after you rest it and your wallet only had ten pounds in it anyway. Someone who's irrational can jump to the conclusion that "Well, Uranus is in line with Neptune today, which means that it was God's will that I suffer today."
Atheism does not, as you say, impart any level of improved IQ or understand by being Atheist. Remember, Relians are Atheists by definition, and believe the exact same thing Christian Creationists believe - just replace God with super advanced space lizards. Atheism, unlike religion, tends towards open-mindedness rather than arrogant stubborn-ness that a two thousand year old book holds the answers. If your response to evolution, the universe and morality is 'God did it' without questioning it, then you're not going to learn. Being religious does not bring you any closer to enlightenment. Christianity is saying a man in the sky made the universe for some reason which you don't know, because you're an imperfect sinner. This is the same level of understanding of the universe as a child pointing to the sky and saying 'Look mummy! Big cloud makes pretty sun go across sky, yay!'. An Atheist and a Christian are equally able to pick up a book on the physics of the universe and learn about the wonders of the galaxy we live in. The difference is that Atheism doesn't claim to know the answers. Christianity does. When you have the one answer to slot into all situations, why pick up a book to learn about the universe? You have the Good Book.
Being an Atheist does not grant you skepticism and rationality; being skeptical and rational tends to lead people towards Atheism. A skeptical person, when told that God is a good being and is shown doing what he does in the Bible tends to question that being's morality.
I'm not even going to comment on how silly the idea is that all Atheists are just attention seekers trying to cause trouble. Especially when you consider that religion does, in fact, do this ("We need to cause a big fuss over a man marrying another man! This is disgusting! My book says so! Pay attention to me! You must do something about this, government, to appease my two thousand year old book's ideals!")
People have always found a reason to kill one another and an excuse for the crime. Religion, culture, ideology are all quickly used culprits for such things. I doubt few of the atrocities attributes to religion have really anything to do with actual religious dogma or belief. Most such atrocities can be easily traced to human emotion and desire over any lofty notion of performing Godís work. Nearly every religion no matter how peaceful can be traced to some atrocity. Likewise nearly an ideology, atheism included, can be linked to genocide and atrocity. The common denominator being humankind, not religion.
Religion isn't a sole reason. It is, however, another possible justification. Are you saying that Christianity isn't to blame for the witch-hunting trials? Or the Crusades? Because I certainly recall Christianity's idea that people were 'witches' wasn't something that Atheists created. All atrocities are traced to human emotion, religion is simply the justification. Religion is a very easy scapegoat to make an enemy of another people. "Kill all those people, rape them and take their stuff!" doesn't incite violence and fervour quite like "This is God's will! Kill the heretics! Oh, also, if you find any women or money on the way, God will turn an eye on you, this time... it's a reward to those who are faithful and do his work."
And no, Atheism cannot be linked to genocide in any way. Religion has distinct points which can be linked to why people have done their evils. I would like you to point to one instance where someone's lack of belief in a God caused them to murder women on the suspicion that they were using magic, or that they were 'the superior race'.
I do not think Cyrano is trying to lay low atheism or hold up religion, but is instead trying to convey that the absence of religion will not necessarily make the world a more peaceful place. Certainly without religion people will not be able to claim their enemies are demons. They will simply claim their enemies are of a different nationality, different creed, different background, different tribe or one of many other reasons humans have already given. People have used social-class as reason to kill one another in the past. Religion is simply one scapegoat among many.
Yes, and guess what? People who murder other people for whatever reason are punished. As you say, this has always existed and always will. It's human nature.