For evidence of the irrationality of intelligent people, I proffer the example of every pointless university faculty departmental meeting, ever.
Becoming a corrupt government official and lining your own pockets at the expense of the rest of the population isn't necessarily a dumb thing, nor is working in an oil company or developing weapons for the military. Every dictatorship through history has had scientists and academics working for them on all kinds of horrific things.
That's not saying intelligence can't help fix problems or that being dumb is good. But being selfish or evil or sociopathic doesn't seem to have a lot to do with your intelligence, and the issues often come down to selfishness, greed or a lack of morals more than anything else.