Something else I noticed: After all the flock he gets here every game, about how his suicidal passes cost us goasl and games, how often has that really happened in important matches? I can only recount the Bayern first leg, and even that took a crazy deflected longshot for that to happen.
I mean I subjectively feel safer with Marchisio in his position as well, but there is a reason why Allegri doesn't even seem to consider benching him, and I refuse to believe it's because he's scared.
Our defense is so excellent that the giveaways aren't such a big deal. I've seen Marchisio, Vidal, and Pogba also give the ball away quite a few times this season, although Marchisio never seems to give up the ball when he's playing in that Pirlo position, it's always when he's playing a little wider and further forward.
The bigger liability with Pirlo in that position is that he offers nothing marking runs of their players into the box. He leaves our defenders stranded. The Ronaldo header in the first leg was a completely free header, because Pirlo didn't bother to follow him. And again, he didn't stay with James, he let him just cut into the box and take Chiellini on 1v1 which is always dangerous for us. Marchisio provides much more help for the defense.
That being said. His presence is incredibly calming for our team, and in a match this big, that's a good thing. The other thing is that Barca is much more susceptible to long balls over the top than Madrid IMO. So if his long balls are accurate he could play a very key role there in freeing Morata and Tevez going forward.