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. There's playing on the counter attack and then there is trying to park the bus ala Jose Mourinho last season when Inter defeated Barcelona on their way to winning the Champions League.
It also doesn't help that Arsene Wenger is clearly incapable of matching Mourinho tactically.
This is an extremely talented and offensively dangerous Barcelona team, but they are vulnerable defensively and thus, beatable. Arsenal refused to even try to exploit that weakness and they paid the price with the result. You can cry about the injustice of the red card or the fact Abidal escaped punishment for pushing Van Persie in the throat all you want, doesn't matter. Arsenal didn't even try to play the game.
Instead of potentially pulling off a tremendous upset, they'll grasp at the scapegoat given to them by Busacca's questionable performance. Fans can bitch and complain about referees to their heart's content (I certainly do) but from a player and coach' perspective, going to the extremes that Van Persie and Wenger apparently did accomplishes nothing, other than making you look like a someone desperately grasping at excuses.
Arsenal didn't even attempt to play Barcelona last night. They had zero shots on goals and only scored because of a Sergio Busquets own goal. Everyone knew Barcelona would dominate possession but instead of picking your spots and exploding mistakes like they did in the first leg, Arsenal sat back and tried to hold on. That's not good enough and no matter what the referee did or didn't do, there is no one to blame but Wenger for making a poor tactical decision.
He should know his team is not the type of group capable of bunkering, he should know that Barcelona could be exploited defensively. It's impossible that he didn't, so that means he chose to attempt to park the bus anyway, despite the fact his team isn't built for that style of play.
Seems pretty clear why Arsenal hasn't won any silverware since 2005 since your manager is sitting below a glass ceiling, lazily hitting it with a feather duster.