I can see benching all of those you cited, Marlo, with the exception of Demarco. While he is going against an underrated Seattle defense, their greatest strength is in their secondary. They can be run on and Murray looked as good as any back in the league in Week 1. And, really, he's been a monster in pretty much every game he's played in during his brief NFL career.
I'm all for gambling with matchups and Morris looks to be a solid RB2 for at least the first part of this season (we'll see how things go after Week 8), but I wouldn't sit a stud like Demarco for him.