I have just read a wonderful critique of 'libertarian paternalism' by
Gary Becker, complemented very nicely by
Richard Posner. Some excerpts from both texts below (which also attempt a summary of the main arguments):
The term is indeed an oxymoron. Libertarianism, as expounded in John Stuart Mill's On Liberty, is the doctrine that government should confine its interventions in the private sector to what Mill called "other-regarding" acts, which is to say acts that cause harm to nonconsenting strangers, as distinct from "self-regarding" acts, which are acts that harm only oneself or people with whom one has consensual relations authorizing acts that may result in harm. So, for example, if you are hurt in a boxing match, that is a "self-regarding" event with which the government has no proper business, provided the boxer who hurt you was in compliance with rules--to which you had consented--governing the match, and provided you were of sound mind and so could give meaningful consent.
Paternalism is the opposite. It is the idea that someone else knows better than you do what is good for you, and therefore he should be free to interfere with your self-regarding acts. Paternalism makes perfectly good sense when the "pater" is indeed a father or other parent and the individual whose self-regarding acts are in issue is a child. In its more common sense, "paternalism" refers to governmental interference with the self-regarding acts of mentally competent adults, and so understood it is indeed the opposite of libertarianism. The yoking of the two in the oxymoron "libertarian paternalism" is an effort to soften the negative connotation of paternalism with the positive connotation of libertarianism.
(Posner)
A serious problem arises if libertarian paternalism is not just considered an intellectual exercise, but is supposed to be implemented in policies that control choices, such as how many calories people are allowed to consume, whether adults are allowed to use marijuana or smoke, or how much they can save. Even best-intentioned government officials should be considered subject to the same bounds on rationality, limits on self-control, myopia in looking forward, and the other cognitive defects that are supposed to affect choices by us ordinary individuals. Can one have the slightest degree of confidence that these officials will promote the interests of individuals better than these individuals do themselves?
(Becker)
One of the great weaknesses of "libertarian paternalism" is failure to weigh adequately the significance of the operation of the cognitive and psychological quirks emphasized by libertarian paternalists on government officials. The quirks are not a function of low IQ or a poor education; they are universal, although there is a tendency for the people least afflicted by them to enter those fields, such as gambling, speculation, arbitrage, and insurance, in which the quirks have the greatest negative effect on rational decision making. As Edward Glaeser has pointed out, the cost of these quirks to officials--who are not selected for immunity to them--is lower than the cost to consumers, because the officials are making decisions for other people rather than for themselves.
(Posner)