I think the mankad should be part of the game, however I believe a warning should be delivered first.
I feel this should be the case because unlike other dismissals, you are not beating the batsman on your ability.
Whilst some batsman are trying to steal a yard, see Jos Buttler vs SL, I feel it is harsh on someone backing up in normal manner and at most can be accused of carelessness, see the U19 WC mankad.
After a warning, no batsman has a leg to stand on.
My personal worry with changing the rules is that we'll see it more often in club cricket. I don't think umpires I have played with would know either way if the batsman was out or not. Another reason why a warning may be suitable. A warning being as easy as informing the umpire/non striker that if he doesn't be careful you will mankad him, although appreciate a physical warning would make sure everyone was aware.