I'm not the biggest fan of Barkley, but just because he attended USC doesn't mean he's doomed. What exactly does Pat O'Hare failing in the pros have to do with Matt Barkley? Did they have the same coach, run the same offense, have comparable measurables? Should teams avoid every LSU QB for the next thirty years because of Jamarcus Russell and Matt Flynn? Should teams go after QBs from Stanford because of John Elway and Andrew Luck? Let me guess, you were convinced Chad Hutchinson was going to be the next John Elway because of his alma mater. Can you name any great guards to come out of North Carolina? I can't off the top of my head. Better avoid Jonathan Cooper at all costs.
It's silly to base even part of an evaluation of a current player on players from 30 years ago who's only similarities are their positions and the school they went to. Mark Sanchez failed because he wasn't very good, same with Leinart, Barkley could fail just like them, but it won't be because he went to USC.