That's a bit of a stretch. It isn't without (legitimate) criticism --as any work of this scope is-- but Diamond is mainstream, and the book has won several scientific awards and a lot of praise.

The over-arching premise, that luck and circumstance played a huge role in the development of civilizations, isn't really disputed. And there are lessons in there for today: not everything you've earned is a product of your abilities.

Indeed it is but mainstream historians and anthropologists are not the arbiters of good science. The criticisms, that I'm aware of, come down to incomplete research on Yali (not a critical aspect of the narrative and absent from The Third Chimpanzee) and an over-enthusiastic pre-emptive argument against a neo-darwinian interpretation of genetic data.

I agree with carterklein13, Guns, Germs, and Steel is near the top of my list of influential books.