Having covered the libertarian and liberal vices, this one seems only fair. Of course these vices change with the times, but the current conservative vice I would describe as follows:
Using meritocratic arguments to reassign marginal products
It is best explained by example. An anti-war liberal will say "Our occupation of Iraq has gone badly. Things are worse than under Saddam." In addition to contesting this comparison, many conservatives will respond: "But if the Iraqis weren’t so intent on killing each other, they could have a decent society, just like the Kurds do." The claim is true, but it represents an attempt to reassign marginal products away from one policy and toward some other infra-marginal fact.
Or consider domestic policy. Policy X does not make a dent in the poverty rate, and this is pointed out by a critic. A conservative might respond: "But if those people would live by Confucian or Korean family values, they would do just fine."
The conservative vice is not intrinsic to conservatism, but I see it to an increasing degree. Perhaps it is a response to the combination of a nominal conservative majority in goverment yet a growing inability to control events.
This intellectual move is not in every case false. If we are considering the relative obligations of citizen and state, for instance, it must be recognized that a state can do only so much for self-destructive citizens. But when the vice is "applied" to situations where a more consequences-oriented approach is warranted, well, then it becomes a vice.