My opinion on humanity, this great and varied species of ours, is largely dependent on my mood of the moment. I guess the defining characteristic of h.sapiens sapiens is his astonishing range of potential for both good and evil.
We're the species that has harnessed the power of the atom, that fights back death and disease and age every year with the power of intellect, and that has produced individuals like Beethoven, Shakespeare, Einstein, and Thomas Jefferson. We are not the strongest species on this dirtball, but we have that effective combination of intelligence, dexterity, and ability to learn that makes us the undisputed masters of this particular domain.
Yet we are also the species that has mastered the art of exterminating each other. For every genius, for every monumental triumph of science, for every enduring work of art, humans have also produced an Auschwitz, a Wounded Knee, a Battle of the Somme, a Srebrenica, or a Kristallnacht. We are not the only species on this planet that routinely kills each other, but we're the only species that routinely kills each other for sport, for pleasure, for profit, or for purity of theology.
I am still undecided on whether we're too intelligent, or too dumb for our own good. I mean, we have the brainpower to split atoms and make footprints on the moon, but at the same time we fall prey to mysticism--which, in its mild forms, manifests itself in harmless things like mood crystals or prayer clubs, but which in large doses makes people strap nail bombs to themselves and entire countries slaughter each other with dedication.
It is said that the oldest profession in the world is the prostitute. If that's the case, then the second oldest profession in the world is the shaman, the Mog-Ur, the priest, the cleric, or whatever you want to call his particular sort. He's the guy who tries to help people make sense of the world around them, and who attempts to make the unknown knowable. He's the guy who understands that his job is a way to social status and power, and he's the guy who collects the sacrifices on behalf of God, or Allah, or Odin, or Ahuramazda. He's also the guy who makes sure the young ones learn all about the importance of the thunder god early, so that the shaman's job may be secure for another generation to come. Lastly, he's the one who tells the young men of the tribe to paint their faces and prepare to punish the unbelievers.
Why are we as a species so susceptible to having our emotions override our reason? What biological circumstance can make a mild-mannered accountant put on a uniform and kick the gold teeth out of his neighbor's mouth? What kind of faulty wiring can enable a person to write a poem or play the violin in the morning, and then in the evening hang another man from a tree or shoot him in the head in front of his children?
I think part of the reason for our astounding capacity for cruelty lies in the way we form social bonds. We can communicate with each other at the speed of light and across this planet, but our brains are still hardwired into the social patterns of the neolithic campfire. We have a need to identify with a tribe, so we define our own tribes, even in the twenty-first century. Of course, the second thing after identifying your tribal allegiance is to identify "the others", those who are not of the tribe. It doesn't matter what one takes to be his tribe--nationality, skin color, profession, sports team allegiance, language group, religion--once you have established the "us", you proceed to establish the "them", and the most natural instinct in the world seems to be to defend the "us" from the "them" by any means at one's disposal.
Take professional and college sports as an example. Here's a tribal allegiance that is as close to its neolithic template as possible. You have two tribes that engage in a ritual battle with each other. You have easy identifiers: face paint, clothing of a specific color, battle songs, and banners. You have a supportive population which cheers you on, and which promises increased social status and recognition for victory in battle. Finally, you have a clearly defined battlefield, an elaborate ritual, and a contest of strength and skill before the eyes of your friends and loved ones. How much more warlike and emotionally satisfying can it get? It appeals to our deepest instincts of security, survival, and social standing within our own tribe. (That's why we have hooliganism and violent excesses at soccer games or college football events--once you stroke that lizard part of your brain with the right stimulants, it's easy to temporarily forget that you're not fighting an actual war.)
It looks like the way to get that mild-mannered accountant to willingly become a concentration camp guard is to promise him increased social status, and to grant him moral absolution for his actions. The human need to belong and be recognized is a strong one, maybe the strongest motivator there is, and any reward system that taps into it has the potential to become nearly irresistible. Witness the willingness of the world's young men to not just kill each other over tickets to the afterlife, but the willingness of many to kill themselves in the process as well.
So what's the solution to this particular problem? I don't think there is one, to be realistic. It's easy (and especially tempting for a nonbeliever like me) to implicate religion, for example, as the main source of strife in the world, but religion--every religion-- is afflicted with the same duality as the species that practices it. At its best, it fosters and encourages love and kindness and charity...and at its worst, it brings us pogroms and sectarian killings and decades or centuries of warfare over whose invisible friend is the most powerful. (Those who wish to blame our current problems on a particular religion only succumb to the pitfalls of tribal thinking--the emotional satisfaction of seeking a simple answer to a complex problem, one where the enemy can be easily identified by a common and obvious characteristic, so we may know which people are of not of our tribe.)
In the end, I think I prefer to think of our species as the race that produced Galileo and Da Vinci, and think of the Mengeles and Torquemadas of history as aberrations, victims of overdoses of nationalism or religion or power, overdoses that short-circuited the reason and logic parts of their brains. Maybe that's what makes the heights and triumphs of our species even more impressive--the fact that our species as a whole, and each member of it individually, has a choice between luminescence and savagery every day, and that our high marks were achieved despite our ever-present tendency to let the beast off the leash. After all, someone incapable of doing violence cannot claim credit for peacefulness anymore than a eunuch can claim chastity as a virtue.
Maybe one day, when our species has "clawed its way out of the mud and spread itself among the stars" (to speak with Heinlein), our brains will evolve to the point where we have the ability to define our tribe as "humanity", and where killing someone else over nationality, skin color, religious beliefs, or dietary habits will be regarded as ridiculous as throwing a virgin into a volcano to placate it.