We've done remarkably well.
But we're not designed for this life. We still have all sorts of crap in our genetic and psychological makeups that gets in the way. Ideally humans would be almost purely rational, acting logically for the betterment of themselves and mankind as a whole. You could throw in a little irrationality for the sake of art and keeping things interesting, but while we're all appreciative that Yo-Yo Ma spent his time mastering the cello instead of, say, working on a farm, other irrational behaviors aren't nearly as appealing. From smoking to rape to suicide bombings, the monkey behavior can have some pretty grim fallout.
And the thing is, humans are pretty good at acting rationally when it comes to themselves compared to how they are when dealing with larger issues. Most people manage to feed themselves, control when they reproduce, and generally manage their own lives decently well. But almost everyone who deals in major issues falls into one of several traps.
The first of these traps is to overassume your own importance, and that of whatever you're looking at. People like feeling important, but they also tend to give importance to features that are salient (This is why people think tall good-looking men are smarter and more competent than short dumpy men, even though there's little to no correlation in general, and certainly not enough to make assumptions in an individual case. Tall and good-looking are much easier to see than smart or competent.) Whenever you study an individual problem for any length of time it becomes very salient to you, and it starts to take on added importance and gravitas.
This is why Al Gore overstates the case for global warming (not the chances that its happening, but the likely outcomes from it), somewhat undermining himself. The more he looks at the data the grimmer and more important it starts to look, and the more extremist his viewpoints become. This is why economists are routinely overconfident about the predictive power of economics, even when the limitations have been shown time and time again. This is why the Iraq war planners thought that the thing would go off without a hitch. They spent a lot of time looking at America's strength and started seeing her as invincible, able to win any war almost magically without sacrifice or even much planning.
Another thing humans don't deal with very well is uncertainty. We want outcomes, not probabilities. This served us well as monkeys, when we were dealing with small, local, events and it was better to believe there was a bear in every cave than to calculate the actual probability of a bear being in any individual cave. But when dealing with big, global, events, almost nothing is certain. We don't know how things will play out. We can look at global warming as a looming disaster, which it likely is, but 5 years from now some scientist in France might invent a bacteria that traps carbon emissions, and suddenly it's much more manageable without us having to cut down. We look at peak oil and it's scary as hell, but tomorrow someone might come up with a more efficient extraction process for low-quality oil fields, and buy us ten years. We look at America and think it's powerful and will last forever, but that's what the Romans thought about Rome. And there are barbarians at the gate. And we don't know if we can beat them.
In addition to all of this stuff comes the petty human crap of wanting to seem important and wanting resources for yourself. So scientists fudge data to get research grants and research assistant pussy, and politicians lie cheat and steal to pad the pockets of their friends etc...etc.. Humans are venal creatures and that doesn't look like it will turn around any time soon. No society is close to perfect.
I just wish that we as a species would take better and more complete stock of our flaws and calculate them into the things we do. Because when we make assumptions like we're perfect, well, that's frequently when you get tragic consequences. The Soviet Union was built on the idea that a bunch of humans could run things rationally for all the other humans and it would all work out swimmingly. Not so much. Government programs tend to bloat and corrupt, mostly for the reasons I stated above. Brilliant people can fall victim to their irrationalities without corrective forces.
If we accept that we're overgrown, fundamentally flawed, monkeys that won't make all these problems go away, but it will help us recognize when they're getting in the way and try to course correct for them. And that will be another step towards acting rationally, as a species.
Or we could just blow each other up over competing desert-people mythologies. That works too.