Well, seeing Vol'Jin being the traitor after all is not so wrong. Garrosh was worried that Vol'Jin can turn out to be a traitor to the cause, so it's dangerous to keep him alive. But Vol'Jin survived, and... what, he turned into a traitor of course
Gotta say I'm on Garroshes side here - as always. If he sent a better man for the job, the Horde would not be torn apart by some rebellous trolls!
And, by the way: every time I see Cairnes death being mentioned as a proof of Garrosh being bad and evil I'm looking around for some small animals to kill. CAIRNE challanged Garrosh. He did it basing on FALSE inter he DIDNT EVEN BOTHER TO DOUBLE CHECK. Garrosh offered to change the duel into a death battle to scare the opponent away, but Cairne ACCEPTED. In short, Cairne acted like an idiot and paid with his life.