I don't really have an abstract objection. Personally, I think individuals differ in maturity and what's appropiate for A isn't necessarily appropiate for B. I may particular objections for one person or another. However, as a legal issue we set limits only because as a matter of law we can set individual limits.
Think of my view like an American Express card - a number of factors go into a particular decision to accept or reject charges rather than having a set credit limit.
I should write only when fully awake - that should read - we have to set group limits because as a matter of law we can't set individual limits. That being said, it isn't necessarily wrong for an individual (purely on ethical rather than legal grounds) to behave in a particular way considering the totality of the circumstance.