We are paternalists when we make someone act in his own interests. - Derek Parfit

To think about reality we must use concepts, and certain truths about concepts may reveal, or reflect, truths about reality.

Why shouldn’t I eat toothpaste? It’s a free world. Why shouldn’t I chew my toenails? i happen to have trodden in some honey. Why shouldn’t I prance across central park with delicate sideways leaps? I know what your answer will be: “it isn’t done”. But it’s no earthly use just saying it isn’t done. If there’s a reason why it isn’t done, give the reason—if there’s no reason, don’t attempt to stop me doing it. All other things being equal, the mere fact that something “isn’t done” is in itself an excellent reason for doing it.

When some principle requires us to act in some way, this principle’s acceptability cannot depend on whether such acts are often possible. We cannot defend some principle by claiming that, in the world as it is, there is no danger that too many people will act in the way that this principle requires.