There is a difference between a rat and a pest. Brad Marchand is a rat. Antoine Roussel is a pest. One guy drops the gloves when someone approaches, evidenced by his 7 fights in 2012-2013, 10 fights last season, and 6 fights so far this season. The other runs away after throwing cheap shots and hides behind bigger players like Chara and Lucic, as evidenced by his 5 total fights for his career, including 0 last season and 0 so far this season.
This logic is also insane to me. They both toe the line, but one is excused because he's willing to punch the other team's enforcer in the face after he does it? Really?
I have no moral opposition to fighting. I don't care that it's barbaric. I just don't see the point in it anymore. Hockey is no longer a game of brute, physical intimidation like it was in the '70s and '80s. And it's better this way. If a team gets an advantage by playing the opposition's stars physically, they will keep doing that regardless of which talentless goon they send over the boards to "protect" them.
People whine about how much more honorable the good ol' days were. But the good ol' days had regular stick swinging incidents, bad hits, bench brawls, etc. Yeah, fighting really kept the game clean!
EDIT: And, oh, one of those players is a top six forward and a core contributor to his team. The other is nothing but a ball of energy. It's no wonder that one fights more than the other.