That certainly was not why Fernandinho was red carded. Everyone was dragging everyone away in hopes of breaking up a fight in that scuffle. There was no malicious intent at that point. And two wrongs certainly does not make a right as if it is justification to a retaliation slap.

If that's all you can see and then feel free justifying your feeling good with confirmative bias.

Fernandinho was an idiot for his overreaction to the slap but Fabregas is no saint either.