You Should be Blaming Wenger, Not the Referee

There are plenty of Arsenal fans that are still screaming until they're red in the face about referee's Massimo Busacca to send off Robin Van Persie...but you're missing the point.
Arsenal's stubborn determination to sit back and defend their lead, rather than even attempting to attack a Barcelona defense that was weakened by injuries was the difference in the match, plain and simple.