The guy I blame more than anyone else for that fiasco is Moises Alou. If he'd simply shrugged off Bartman's interference and gone back to his position like nothing happened, the inning might have turned out differently. I believe Alou's angry, glove-throwing overreaction completely unnerved the Cubs and the fans- and inspired the Marlins.
(Also, why the didn't Dusty Baker visit the mound to check on Mark Prior, especially after he walked Castillo on a wild pitch right after the Bartman play?)
However- and I don't condone the way he was treated by Cubs fans one bit- I do blame Bartman to a certain extent. Every fan ought to know the old rule- when it's your guy making a play on a pop fly get out of the way, and when it's the opponent making a play on the ball get in the way. He had no business going after that ball. I mean, the Cubs are five outs away from the World Series and he's thinking about a souvenir? His priorities were completely out of whack.
The whole Bartman thing is an example of a sports "curse" perpetuating itself. The reality was that the play changed nothing in the game- there was still a man out, a man on and a 3-2 count on Luis Castillo, which was exactly the situation before the play. There wasn't even a guarantee that Alou would have caught the ball. But since it was the Cubs, since it was Wrigley Field, it was as if everyone was just waiting for something like this to happen. The "curse" is the expectation that the other shoe is going to drop at some point and the way the bubble immediately deflates when it does. There was no reason the Bartman play should have caused such a meltdown. But it was almost as if the Cubs and their fans willed it to happen.