Nicely done by Roger L. Simon:
That reason is moral narcissism, the underlying motivation behind what Andrew McCarthy so accurately calls "willful blindness." Bernie is willfully blind about Israel, even though he spent time on a kibbutz and still has relatives in the country.
This moral narcissism that grips Bernie -- unlike the traditional narcissism of Narcissus admiring his handsome reflection -- is a narcissism of ideas and opinions. The views that make you feel good about yourself, that make others praise you and make you part of the "club," are what is most important to you and your self-image. They literally define you. Whether those views are based in fact or whether the results of those views are the least bit salutary is immaterial.
The moral narcissist, therefore, is almost always blind to reality, indeed disinterested in it. It's the pronouncements that count and are real. Moral narcissism leads inexorably to politically correctness. It is, in fact, the mother's milk of political correctness.