We're only a quarter of the way through this round of the Champions League, but by far the two best ties—Barcelona vs. Manchester City and Bayern Munich vs. Arsenal—are all but technically over. And while neither result is necessarily surprising, it's unfortunate that both matches turned on the controversial red card-penalty double whammy that needs to be changed.
First, let's look at the challenges themselves. Above is the Martín Demichelis tackle from behind on Lionel Messi. This was the more straightforward of the two incidents, as most non-Mancunian spectators agreed that it was a stonewall penalty and sending off. (For you "He was outside the box!" truthers, the tackle did continue into the penalty area and otherwise was so close that there was no way for the ref to have seen it in real time.) But even then, the play wasn't dangerous, which is really the only time a tackle should earn a red.
Next, we have the collision between Wojciech Szczesny and Arjen Robben that had Arsenal's keeper mockingly playing with himself instead of with his teammates. This one was more debatable. Yes, it too was an obvious penalty, and under the current rules Szczesny was justifiably, if a bit harshly, sent off. But this situation makes the rules look even worse. What else was Szczesny supposed to do? A defender's error in the box shouldn't see him red carded just because the attacker is more clever in that moment. In fact, there wasn't too much of a difference between Robben besting Szczesny and Mesut Özil getting clattered by Jerome Boateng for Arsenal's penalty. Getting fooled shouldn't get you sent off.