I have a hard time understanding Luiz's red card. I think he's pretty masterful at the dark arts and wouldn't mind trying something like that in another situation, but I don't see any way that was calculated or intentional. Incidental contact is the standard for a red card and a penalty? Eh... Not the game I want to see.
Thinking about this more it just seems like a poorly written rule. The double jeopardy exception as written into the rules is spelled out specifically for situations in which the player attempts to play the ball but commits a foul. Its meant to cover non-intentional fouls, but its not written broadly enough to cover non-intentional fouls in which you don't attempt to play the ball, probably because they're very rare.
By the spirit of the law, there is no way this should be a red card. The whole point of the double jeopardy rule is that you shouldn't penalize send off a player unless they intentionally tried to impede a goal scoring opportunity. By the letter of the law, I think the referee's only two options were to say it wasn't a foul at all or to award a red+penalty.
I'm obviously biased but I think the genuine correct call would have been no foul. That kind of incidental contact very rarely gets called in the rest of the pitch. Its a physical game, players are constantly running next to each other, parts of their bodies nipping each other when they run. It can't be a foul to unintentionally touch another player's leg while you're both running. But I can see why the referee would have a hard time making the right call there, especially once he had already made the initial decision.
Mainly, however, its just a poorly written rule. Clearly the referee should have discretion to award a yellow for non-intentional fouls that don't involve playing the ball.