I don't get how Thiago is easily allowed to be blamed for leaving, yet Cesc isn't?
Even if cesc was to blame aswell (I'll explain later why he isn't) the fact remains that thiago has left while cesc is still here, as a Barca fan you should support your own player over a player who has left you for a champions league rival. There is no reason for the thiago vs cesc agenda on ether side to exist anymore yet some insist on continuing it.
As for the other part... Thiago is clearly rated by our club and was being groomed as the successor to Xavi. Even if cesc arrived his development was proceeding as planned and it looked as if we had our midfield secured for the future. Thiago was at an older age and on the brink of regular football, before dumping the club.
Cesc on the other hand wasn't rated so highly. He knew that he probably wouldn't get games over the other young talents, who were better than him at the time. Also remember that he was only 16 years old and not exactly on the brink of first team football, he knew his departure wouldn't have hurt the club, as he wouldn't have been a starter for years to come anyway. He saw a unique opportunity fom arsenal that he couldn't refuse, and it was only later that he surpassed the other talents through his development there.
See the differences here? Thiago was our main talent and knew we had groomed him to be our starting midfielder over Xavi, only to dump us at the last minute. Cesc is a total different situation and you can't blame him for it, he wouldn't be where he is today if he hadnt done so.