There are always going to be cowboys around, but IMHO there are far less N reg cowboys than G reg ones (I've seen people bolt a new prop on after a prop strike and not tell anyone - on the G reg!!). We can't afford to be for the reasons IO pointed out before.
Also most N reg pilots in Euroland are better qualified, and probably a high proportion of them have an IR.
No reason to restrict N reg's at all IMHO.