I think it's okay to campaign hard in the primaries and have strong preferences. Even if your candidate doesn't win, that strong show of support of their values and policies will spread to the rest of the party (see: everyone picking up Sanders platforms that would have called him a crazy old man a couple years ago (though still calling him crazy while picking up his policies))Twitter overall is garbage. In the end, I agree it's about who you support. I'm very much a fan of Beto, because I think he's the perfect candidate to beat Trump for a multitude of reasons. But could I easily hop on the bandwagon for Kamala or Pete or Warren? Sure.
It's ok to have preferences. To be a "Candidate X or BUST!" kinda person, especially at this stage in the game, is a bit nuts.
The amount of people who would not vote or vote for Trump in 2020 if bernie didn't win is small, and will be completely overtaken by new "fuck trump" voters anyway. People are passionate about having the most progressive candidate with the most progressive record because time is running out, and we need bold changes soon. Just beating trump and expecting the rest to follow isn't enough for many people