The clearest symptom of this intellectual laziness is making arguments for specific exceptions that imply far broader exceptions. Even libertarian heroes like Milton Friedman have been guilty here. How so? Let me outsource to the noble Don Boudreaux.
I am convinced that Milton Friedman's most regrettable contribution to
public policy is not the relatively minor role he played during WWII in
implementing a system of income-tax withholding in the United States.
Rather, his most regrettable contribution is announcing that, while he
favors open immigration in principle, he opposes it when the home
government runs a welfare state...
[A]s far as I know Friedman never qualified his passionate, powerful, and principled case
for drug legalization by claiming that legalization, while desirable in
principle, is unworkable (or undesirable, or impractical, or
unrealistic, or whatever) in a world with a U.S. welfare state. But it
seems to me that if Friedman genuinely believed that the existence, and
likely permanence, of a welfare state in America is a strong-enough
reason to empower government to do what that government otherwise ought
not do - in the case of immigration, forcibly prevent people from
migrating to the United States - then he should also have qualified his
argument for drug legalization with the same condition; namely, in the
case of drugs, forcibly prevent people from getting high by whatever
peaceful means they choose.
The fact that Friedman (again, as far as I know) never qualified his
case for drug legalization with the condition that the welfare state
first be rolled back suggests to me that Friedman's case for restricting
immigration (at least as that case has now come down to us in lore) is
at odds with his case for drug legalization.
And, while we're at it, doesn't the existence of the welfare state
require government also to restrict which majors college students
choose? Without a welfare state, students would be more focused on
finding gainful employment after they graduate. But with a
welfare state, the risk of being unemployed for long periods - or of
earning very low pay for most of one's working life - as a result of
majoring in the likes of "race studies" or "dance criticism" will too
often be ignored by irresponsible or lazy students, who rely upon
welfare-state payments to subsidize their indulgence in majors that
promise no decent monetary rewards.
Where does the enhanced scope for government action end once we admit
that government buys for itself, by illegitimately exercising power W, an indulgence for the exercise of otherwise illegitimate power R?
What sort of distrust of the motives and knowledge of government
officials leads many self-described libertarians to oppose government's
exercise of power W but approve of government's exercise of otherwise-illegitimate power R if government insists on simultaneously exercising illegitimate power W?
Obviously, you could try to make the case that the perverse interaction between the welfare state and immigration is more dire than the perverse interaction between the welfare state and drug use or college major selection. But I've yet to see any except-for-immigration libertarian carefully construct such an argument. Why not? If you have an explanation for these missing arguments other than intellectual laziness, I'd like to hear it.