I know what you mean about the studs thing, you look at numerous tackles made over the course of a weekend and technically the studs are up.
But the difference is that one is 2 players going for the ball, and one is throwing yourself recklessly at an opponent with your studs showing. If you make contact you run a serious risk of injuring the other player. Barton done the latter.
Like i said before, at first viewing i thought it was harsh and the ref gave the card based on Bartons reputation, but on second viewing it was warranted.
He didnt throw himself in front of Alonso, he didn't catch him with his trailing leg. Both feet followed by the rest of him went flying into Alonso studs first. So it wasn't just the studs up bit but the whole challenge i'd say got him a red.