This is really not the point - this is a big game. The Hawks obviously ramped up Harvin for this week. They want him out there, because they think he helps in a big way (not because they think they "need" as if they can't win without him). That's why they got him. And I'm sure Harvin thinks the same way.
I agree with the point that if it was at all manageable he would be out there, yes some games are bigger than others - this is unquestionably a big game, almost a playoff game.
Point being (let's leave Hawks out of this) there is something significant under the surface here.
On Harvin, if he's even basically all right, I think owners are back to seeing to see if he plays, then see how he does, then see if they want to start him. Could be week 14 he plays, wait and see, if he gets snaps and does ok, then start week 15. Or push it back a week if he's not ready. Does anyone really think he plays next week? And are people going to start him the first time week 16? See week 12 for how that worked.