It's a law of the game based on facts, his boot is high and he's endangered the opposition player. Your opinion that you believe is backed up by the referee, FA, Mogga etc. is based on an incorrect interpretation of the laws. Standing by that after the fact isn't just about standing by your opinions, it's also disagreeing with the laws. You're more than welcome to do that (though your reasoning is pretty archaic to say the least), the referee however is in the position to apply those laws whatever they are and he hasn't done that.
I think we all agree it was an accident . and probably no action will be taken, but would have had more respect if the player or Mowbray had said that they had a little sadness about it and would try to ensure there was little chance of repetition.. I remember when the game was a contact sport and the very notable thing was that if an opposition player was accidentally injured, the lad responsible nearly always apologised then and there rather than just pretending it never happened.. I'm not advocating the young lad should have both his nuts chopped off, but I am sure if Billy accidently injured anyone, he would have the manners to say "Sorry, pal" and that is all most people really want