First off, he never actually directly killed anyone.
It's not his fault when Crookedstar broke his jaw, since all he really did was chase them- and Crookedstar did confront him, which he really could of avoided in the first place. There's also the fact that Moonflower's mate did literally try to kill Goosefeather by something that had a badger. Not to mention the fact that he can literally SEE and talk to the dead, and visions and prophecies constantly crowd his head. He didn't really say anything to Bluestar that made her give away her kits, that was all her because Thistleclaw was this "Evil and villainous" cat apperantly, and that was all her decision, all he did really was hint at it, including her death also. He was just really when you think about it- this kind of just broken character since the day when he was born, being slowly driven basically insane by all the gruesome visions and talking dead cats that had just existed to him.
I just... feel bad for him I guess. I really do hope that when he died, that he didn't go the the Dark Forest, but to StarClan, where he may be at peace.