The first part of your post contradicts what you've written below and what your original question was. Seriously, do you have a point because it's pretty jumbled.
Again- You asked why any team would trade for a dirty player... now you post the facts that real life gms employed (and traded for) 2 dirty players who weren't as good as this one. Are you arguing with yourself? If so I'll back away and let you and your personalities debate each other, because it seems like you are doing a good job of defeating your own original point.
As for the league standards, you are correct. And as I've said, I really don't like Marchand as a player, even if he plays on the team I root for. But somehow I think that maybe you are a little more forgiving of dirty plays on your own team. I mean, I'm sure if I look I'll see that you made posts asking for the release of Matt Calvert, Dalton Prout, Blake Comeau, Jan Hedja and Jarred Boll, since all were told by the league that they had illegal plays that never should be accepted.
There's no way you'd be a hypocrite and turn a blind eye to those dirty plays, nor would you want those players on your team. Maybe you could point me to the posts you made asking for the release of Calvert.