Comparing football to league or union is pointless. You might as well compare rugby to cricket and not bat an eye that the bowler got bitten in a heated debate.
You arent even allowed to bite in MMA ffs and people are getting knocked out in all kinds of ways.
Rugby is different in any case. Having played rugby extensively, I can confirm that every player on the pitch (apart from soft wingers ) knows the pitfalls of playing. You even expect it.
Ive seen/recieved/given some barbarian moves on a rugby pitch!