Raki, everything we know about evolution is after the fact. But we still know it. Human being's main evolutionary weapon is our large brain. That's a fact. And it has been enormously advantageous in terms of our survival and reproduction, which is all that natural selection "cares" about. That's another fact.

Yes, we are also capable of annihilating ourselves. Well, no species has ever lasted forever.

Yes, our brains can be duped by demagogues. That's not why they evolved though. Any advantage can become a disadvantage if the environment changes significantly.