Like who, for instance? I'm inclined to think a sweeping generalization like that isn't worth the electrons it took to transmit it. Some of them are, certainly, but among all the people I'd consider to be geniuses, the vast majority seem to be well below the nutjob level.
Okay, but if you're going to define your terms to suit yourself, you can make pretty much any claim appear true. I wanted some names. I think we can agree that Nicolai Tesla and John Nash qualify, but how about Max Planck, Neils Bohr, Richard Feynman, James Maxwell, Albert Einstein, Stephen Hawking, Roger Penrose, David Bohm, Ernst Mach, J.B.S. Haldane, Daniel Dennett, Douglas Adams, Richard Dawkins, Jared Diamond, Jacob Bronowski, Brian Greene, Isaac Asimov, Carl Sagan, Kurt Vonnegut, Christopher Hitchens, Charles Darwin... Those are just a few I came up with after a quick scan of the bookshelves around me, and all of them in my considered opinion have displayed genius-level perceptions and insights. Which of them are whackos?