Your question carries the concept to a non-logical conclusion. If a player blows put thier knee tring to turn to fast on a bad field is that the ref fault? No of course not, and yes soccer is a contact sport but the contact is limited and managed. A ref has to decide at what point a play become to aggressive even if the play is legal. That is my point, just because it is legal does not mean it is safe.
How often do you see high kicks called (especially in girls games) even though no one was hit by the foot? Why would the ref call it if a player was not hit? What pourpose does it serve to call that foul if no player was hurt or even contacted with the kick? Of course you know why, it is about prevent it (ther injury) next time! To me this is along those same lines.
