A genius he certainly is, both in linguistics and in his (abstract) political views. But his genius doesn't necessarily lay in being right: it's to be found in presenting strongly a vision of his own, one which people can disagree with with equal strength. It's the ease one can disagree with him which makes him an attractive target, and people often aim to score points by denouncing his well-publicized views without actually stating their own with equal clarity. That's always the easier way.

Edit: for example, it's easier to denounce someone as un-American than to define exactly what is American.