Two words: Brokered Convention.
So you're saying an anti-establishment type is going to go to that establishment's largest event of the year, knock on the door, request that they void 50 states' worth of primary votes, and then somehow make such a shockingly good case that they'll immediately forget he's a fringe candidate that doesn't mesh with their values whatsoever?
And you think there wouldn't be some major repercussions if that happened (such as, "why bother with the primary if they're just going to give it to anyone with a gold axe to grind"?)
Two other words: "No chance."