Well...Sten was already a Reaver back in the Darkspawn DLC days. Coincidence?
I also would like to know if the Qun is actually helping and not just somehow manifesting the problem in the first place. The Vashoth we read and hear about don't seem to be prone or famous for spontaneous fits of homicidal rage. Sten and the Iron Bull, maybe even the Arishok with his table flipping, on the other hand... and don't get me started on the Tal-Vashoth. Going off the deep end seems to be the entire point of them.
This is why I said I don't think we've seen the full force of the Qun. Not at all. Not a bit. We've seen one guy in Origins who went a little crazy after losing his sword, but the Warden helped him find it again. Not really much of an example of the Qun. We saw the Arishok and his men in Kirkwall, but they weren't acting right. Not as the Qun dictated. Think about it - after his death, apparently the qunari renounced his actions. To me, that says that he wasn't representing the Qun the way he was supposed to be - the way the Qun demanded. Then we have the Iron Bull, who is already teetering on the line between Tal Vashoth and qunari when we first meet him and dealing, in his own, personal way, with the idea that perhaps the Qun isn't for him. And then we have the events in Trespasser, and according to a piece of correspondence you find, those weren't sanctioned by the qunari, either.
What this says to me is that the qunari and the Salasari have precious little hold over their people. The events that we hear about, the parts of the Qun we hear about are through the eyes and ears of people whose judgment is already altered or clouded in some way. Sten was perhaps the closest we had to a "real" qunari, as he warranted a promotion to Arishok upon his return, but that was after his exposure to the Warden, traveling with said Warden as a companion, and figuring out what the Blight was. And he might have been made Arishok for exactly that reason - because he went out into the world of other people, and came back relatively unscathed. Not only unscathed, but with useful information and observations about the humans, elves, and dwarves on top of it.
We haven't seen the full force of the Qun because that appears to only exist in Par Vollen, and things are really, really different in Par Vollen, according to the few bits of lore we've gotten about it. We haven't seen the full force of the Qun because all we've seen are pieces of its army, and that's only one facet of the triumvirate. So I can't really make that decision about which side to side with, because I don't think we really know either side, not completely - we know a bit more about Tevinter, but I think there's still plenty to learn in that aspect, too.