If the union wants to defend the few who are thugs then all the players get what the deserve. The union is not some entity that exists in a vacuum. The players are the union and they can make changes just as much as the NHL can. It's not the NHL that keeps trying to maim the players, its the players doing it to themselves. Again, I think that it is the players, union, and NHL's fault.
It doesn't matter where the line is placed. Guys who do things like Thornton did, pass by the "line" so far back they can't even see it or remember passing it. It's time for other players, in this case Bruin players, to really come out publically and flat out say that Thornton was wrong, he's not a good teammate, and he deserves to be suspended for the remainder of the year (for example). Maybe then other players might take notice. But until that brotherhood of covering for each other ends I don't think there is much the NHL can do outside of attempting to suspend players for season(s).