Most of the "hate" directed at Bernie stems from his incompetence and hypocrisy. I actually agree with him about Mello. I don't like Mello's anti-abortion stance at all, but a 50-state strategy is a 50-state strategy. The problem comes from when Bernie jumps at the chance to endorse Mello, calling him a "progressive," and then in the same breath, he doesn't know if the socially-progressive Jon Ossoff is actually a progressive. Bernie then has to, like he usually does, put out a better statement endorsing Ossoff because he fucked up. This happens so often with Bernie it's expected behavior by now. He doesn't know if ____ is progressive, then someone tells him he messed up, so later he releases an actually good statement endorsing ____. His secondary statements don't convince anyone; the damage is already done.
This is the statement he should have released in the first place, but didn't, because it would literally kill him not to put his foot in his mouth:
And then there's the fact that he said that the people protesting Ann Coulter were intellectually weak when his own supporters exhibited similar behavior in Nevada and at the Democratic National Convention. And that's ignoring how he practically insulted his own supporters without even realizing it! My support for Bernie during the primaries lasted all the way until he went after Planned Parenthood. I gave him more rope than I've ever given any political candidate before. I agreed with him more often than I did Hillary Clinton (IIRC, 97% to 93%). The problem I have with Bernie isn't his policies, it's the fact that he's Bernie, and he wouldn't be Bernie without being an incompetent hypocrite who thinks he gets to decide who's progressive and who's not. I wanted to like Bernie so, so, so much. He makes it impossible. Really, when's the last time you saw Elizabeth Warren or Sherrod Brown drop the ball half as often as Bernie has? You haven't, because they know how to get it right the first time.
Also, for caring so much about income inequality, Bernie doesn't seem to understand that babies cost money. That's why abortion is both a social and an economic issue, but good luck ever getting Bernie to understand that.
Barney Frank is right - Bernie is great at alienating his natural allies.