Quel'thalas was destroyed by Arthas. Lordaeron got taken by the Forsaken, who were mostly former Lordaeronians. Yes Llane was killed but that's what happens in war. I'm not gonna try and justify Stormwind but once again, it was war. War isn't exactly fun.
The Alliance is considered a bunch of goody two shoes except they're not when it matters. The Horde is considered irredeemable villains for the actions of a few Horde members yet the Alliance isn't evil for the same reasons. It's always "they acted alone" or somehow justified.