It all comes down to the type of player he is & how long he sticks around. When we signed Joey Porter we all could care less about the baggage & welcomed that "tougher no BS" attitude he brought to the table. But in the end when he wanted out & became a major pain we all had had enough of that attitude. Same will hold true with Marshall.
I know JP and Marshall seem similar...I have just always had the feeling that Marshall has meant well. He really is a big kid, and is in need of some guidance...and I think when given that guidance and stability he can be a good guy. I don't think necessarily the same for Porter.
When you think of "trouble-makers" or what have you, the list is probably
Randy Moss, Terrell Owens, Chad Johnson, Joey Porter, Brandon Marshall, Steve Smith, etc.
But guys like Johnson, Marshall, and Smith, I believe, are just big kids. They want to do the right thing, they just don't always do it.