Congratulations, Real Madrid, 3:0 is a great result and guarantees advancement to the Semifinal. Ronaldo's second goal was impressive.
However, why was there ANOTHER red card given to the opposition's best player?
What have Vidal, Verratti and Dybala in common?
All three received red cards at critical moments in CL matches, and all three were driving attacks against RM out of midfield.
Why have three different referees made such similar decisions?
What you really need to ask is if they were deserved. Dybala deserved to be sent off, not sure how you can even argue that. Vidal's 2nd yellow was unjust, but prior to that he was putting himself at risk and could've been sent off earlier. Verratti was on a yellow already, probably harsh to send him off there, but he shouldn't be putting himself in that position; and, its not like Verratti is the first one ever to receive a yellow (albeit 2nd) for arguing. In other words, he knew the potential consequences. Also, it is another story entirely if you want to suggest the cards received by Verratti and Vidal changed the outcome of the match.
All I'm saying is, it is not so clear cut that these were obvious referee biases in favor of RM. Some RM fans would say the cards their players receive in Clasico matches are questionable and the ref is always favoring Barca. Would you agree? No because there is a case, a legitimate one, that they were deserved.