The Philosophers' Cocoon

In “Philosophy’s
shameful love for the swastika,” Alasdair Palmer offers an explanation for
why some German philosophers “enthusiastically espoused Nazi ideology.” His explanation
goes like this:

John Maynard Keynes once said of
a man that “he has his ear so close to the ground that he cannot hear what an
upright man says”. These philosophers suffered from the opposite problem: their
heads were so far up in the clouds that they could not recognise the blindingly
obvious fact that Nazism meant torture, persecution and genocide. They became
astonishingly stupid as a consequence.

Philosophers are particularly
vulnerable to this form of idiocy, because there is so little content to their
subject. It does not consist in the discovery of new facts, and philosophical
theories are only seldom decisively refuted by anything. Fashion is often the
most important factor in explaining which doctrines come to be accepted by any
group of academic philosophers.

Call these claims the “Ivory
Tower” hypothesis:

1. Philosophers’ heads are so far up
   in the clouds.
2. There is little content to
   philosophy.
3. Philosophy doesn’t consist in the
   discovery of new facts.
4. Philosophical theories are seldom
   decisively refuted.
5. Fashion explains why one philosophical
   theory rather than another becomes accepted by academic philosophers.

Palmer thinks that the Ivory
Tower hypothesis is the best explanation for why some German philosophers espoused
Nazism.

What do you make of his claims
about philosophy? Does the Ivory Tower hypothesis strike you as plausible/probable/true?
If not, why would anyone think that it is?