To be clear, I'm probably one of the only Clinton supporters who's not angry at Sanders even if he is hurting Clinton in the GE polls. He's entitled to do as he likes, and he doesn't owe Clinton anything.
I am angry. Yes, he's perfectly entitled to stay in the race and work to spread his message. Zero problems with that. But he could easily do that without actively hurting Clinton, but that is not what he is doing. He is fairly actively egging his rabid supporters on in their terribly misguided hatred for Clinton. As late as last year Hillary Clinton was almost universally liked amongst democrats. That is far from the case today due to the right, the media and the Sandernistas all advancing the same misguided narrative about Clinton being somehow currupt.