Studs first dives are not acceptable to me, mainly due to the possible level of impact on a players ankles. As for the approach head first, if a player decides to tackle low and put his head in a position where he may get accidentally booted in the head, that's their problem, not mine.
For me its all about a player understanding that if they want to undertake a course of action that may injure themselves, then they have made that choice to risk themselves. If you want to take a course of action (which is not in the spirit of the sport) that has a high likelihood of injuring another player who hasn't made the decision to take that risk,then you have to accept the possibility of sanction.