The worst part is, this isn't the first time. A while ago, Cartoon Network announced that Steven Universe would be doing a crossover with another Cartoon Network show, Uncle Grandpa. Now, Uncle Grandpa is not a bad show, but it's aimed towards a younger audience than Steven Universe is, so a lot of Steven Universe fans hate it for not pandering to them. When the crossover was announced, these same people absolutely lost their shit. They went into full Tumblr panic mode: you know, death threats and fake panic attacks, stuff like that. Not only did they harass the Steven Universe staff (even though the crossover was their idea), they harassed and threatened tons of Uncle Grandpa fans and anyone else who liked the idea of the crossover. It got to the point where the writers actually had to tell them to stop.
Oh, and I just remembered, there was another time when these same people harassed a writer for the show over a minor continuity error. It got so bad that he had to leave Tumblr for good. Yep, lovely people.