Rasmussen and Den Uyl in their book Norms of Liberty contend on p. 47 that certain "traditional [classical] liberals" decided most unwisely to identify political ethics with the entirety of moral law.
As a result, those who wanted to limit government by defining an extensive list of individual liberties ended up butchering or trivializing morality.
On the other hand, those who fancied a more robust morality willy-nilly granted to the state the power to "concern itself with the moral character of the community."
In short, it seems that the former proposed that because the state ought not to outlaw drinking alcoholic beverages, alcoholism is not a vice; the latter, that the state ought to rescue people from alcoholism even if it means outlawing drinking.
Well, if one is to make a mistake, then why not this one? I don't think that, for example, Rothbard is guilty of this, whose Ethics of Liberty stresses such points as:
What we are trying to establish here is not the morality of abortion (which may or may not be moral on other grounds), but its legality, i.e., the absolute right of the mother to have an abortion.
What we are concerned with in this book is people's rights to do or not do various things, not whether they should or should not exercise such rights.
Thus, we would argue that every person has the right to purchase and consume Coca-Cola from a willing seller, not that any person should or should not actually make such a purchase. (98n)
For we are not, in constructing a theory of liberty and property, i.e., a "political" ethic, concerned with all personal moral principles.
We are not herewith concerned whether it is moral or immoral for someone to lie, to be a good person, to develop his faculties, or be kind or mean to his neighbors.
We are concerned, in this sort of discussion, solely with such "political ethical" questions as the proper role of violence, the sphere of rights, or the definitions of criminality and aggression. (152)
Political philosophy is that subset of ethical philosophy which deals specifically with politics, that is, the proper role of violence in human life (and hence the explication of such concepts as crime and property).
Indeed, a libertarian world would be one in which every individual would at last be free to seek and pursue his own ends -- to "pursue happiness," in the felicitous Jeffersonian phrase. (258)
I agree that proper libertarianism is "thin" and offers only a small slice of ethics, if that's what the authors are suggesting.