It clearly was a foul - He was booked - It was a question of was it a yellow or red. INTENT is meaningless - GETTING THE BALL is meaningless. I can come in from the front and get the ball first with both my studs showing and shatter someone's leg but because I got the ball first it isn't a red? - BS. - There is no mention in the rules of the game on INTENT, or ball contact first during a tackle, or Coming over the ball. There is "Reckless" (Yellow) and "Excessive" (excessive force and endangering the safety of an opponent is guilty of serious foul play should be sent off) Dier should have been sent off as well. Anyone that thinks that "Getting the Ball first" absolves you from a card doesn't know the rules of the game. If you don't like it, fine but those are the rules.
The rules used to be even was off but they aren't anymore similarly, tackles that probably were "Legal" 20 or 30 years ago no longer are. Thank goodness cause I would rather spend time and money watching players with skill than some goon like Vinnie Jones play. I like hard tackles, shoulder charges etc, and yes injuries can happen with clean tackles. But chopping down on someone's leg (the motion of McCarthy's leading leg) with a scissor tackle is absolutely endangering the safety of an opponent.