Bernie Sanders is emphatically not a Democrat and doesn't want to do any of the work of building or supporting the party, but when he decides to run for president, he suddenly wants the party's money and infrastructure, only to abandon the party ASAP after the election. He may be fine as a senator, but as a presidential candidate, he's just so utterly loathsome. He's got major entitled old white man syndrome and it makes me lose absolutely all respect for him.

If you're on to a contested convention, you can't directly reflect the will of the primary voters in the first place (because they didn't pick a winner) so I can't really find any reason to object to superdelegates, most of whom are elected Democrats and already literally representing their constituents in Congress, etc.