Why are you mad? Doomsday is a monster who's sole purpose is to kill and destroy. It can't even talk, so what's the problem here?
You can say that about half of Supermans rogue's gallery.
It's no different from Bane. Yeah in the grand scheme of things there are better characters but both Bane and Doomsday were the ones to give Superman and Batman those epic timeless L's.
Joker has gotten over on Batman a couple of times but did he break Batmans back and put him out of commission?
Lex has gotten over on Superman a bunch of times but did he beat his ass so much he died?
There's no reason Doomsday should be in this movie period. He's a Superman villain and he did in fact have a major effect on the characters mythos. If anything he should have been a stand alone villain for a 3rd Superman movie, well after the League had been established and Superman was place as the end all be all to end a threat in case everyone else fails.