Are people mad?
Police officers aren't allowed to just take revenge because their colleagues were assaulted. They can't just go around kicking people in the face when they're on the floor. Do you know how many police officers are assaulted every year? A lot! If every one of them took their chance at a boot to the head there'd likely be a few deaths and a lot if serious injuries in custody every year.
Police officers are meant to be calm, professional, and should deal with the situation at hand appropriately with only necessary force. The courts are the ones who dish out punishments.
Female, ex police, never kicked anyone in the head (or anywhere).