I'll despair for my race if I keep posting about humans as rationalizing animals, so I'm stopping for now. All I can say is that believing humans could be rational was the most irrational belief I've ever had. No longer believing that does not make me rational, but it does make me happy. If you think of humans as a cross between chimps and bonobos, you'll continue to wish they took better care of themselves, their fellow creatures, and their environment, but you'll stop getting frustrated when they act like pretentious apes.
Albert Camus said, "Humans are creatures, who spent their lifes trying to convince themselves, that their existence is not absurd." It's not our existence that's absurd. We're absurd.
Mark Twain said, "Man is a Reasoning Animal. Such is the claim. I think it is open to dispute." He was feeling wry rather than rude that day. He also said, "Oh, this infernal Human Race! I wish I had it in the Ark again--with an auger!" Like many people who've been called misanthropes, Twain couldn't rationalize knowing the human race and loving it.
I'm still working on both parts of that.