Over the years, I have on numerous occasions been rejected personally because of the views that I have, hold, explain and espouse. But I have no similar political litmus test for friendship. It seems to be a one way street, and the further to the left, the likelier one is to limit their potential friendships in this manner. It is these folks on the extreme left that don't simply think that conservatives are mistaken and can be won over with persuasive argument. Attempts at argument have not persuaded the conservative who has heard it all before and reached other conclusions. The liberal then concludes that the conservative is therefore evil in some or multiple ways. Never will they consider much less conclude that their own arguments are ineffective, simplistic or mistaken. It then follows that said conservative must be shunned, ridiculed, rejected, boycotted etc.... because they are evil.
The unfortunate result of this childishness is coarsened rhetoric and an insularity that explains why these folks never seem to think they are wrong or outside the mainstream. Heck, all their friends agree with them.