It's not what you know, it's what you know you don't know
Part of what conservatism has meant, as a political idea, is a circumspect attitude towards knowledge. It is this position of doubt, a claim about the limits of our ability to know, a claim of "unintended consequences."
I'm very sympathetic to this idea, but not persuaded. I find it fails, first, to translate into any coherent political plan or program (how are the unintended consequence of cutting taxes substantively different from those of raising them?). This is especially the case since conservatism and this idea of human limitation has not been parlayed into efforts at preserving a status quo, but has been focused on reversing policies, abolishing or neutering institutions, and radically remaking society in the form of an imagined past. This is surely as ambitious and as unmarked by doubt as any New Deal or Great Society plan. Second, unintended consequences ought to be as pernicious in private action as in public programs, and this seems to be ignored by those who would privatize everything (consider the unintended consequences of Blackwater). Third, I don't see why the unintended consequences should necessarily be negative. That's a move that doesn't seem to have any logical support. Fourth, and finally, the negative unintended consequences of progressive programs, historically, seem to be piddly, when compared to the real, positive effects. Social security saved lives, outlawing child labor saved lives, WIC saved lives, and yes of course there were unintended consequences to these programs, but it's preposterous to say their net effects have been negative.
Maybe more critically, though, it is profoundly odd that a political philosophy that takes doubt and systemic uncertainty as central has consistently found philosophical moorings (or at least common cause) with foundationalist theories. Why, if we believe human knowledge is dramatically limited, would we rally to support natural law, with its claims that right society and correct living are not only completely knowable in all important ways, but also immediately knowable. Why wouldn't we go from "unintended consequences" to postmodernism, where doubt and uncertainty and the limits of knowability are central? Why not something like a "hermeneutics of suspicion"? It doesn't make sense. Philosophically, conservatives have said anything short of absolute certainty is tantamount to and is nihilism, while, politically, conservatives have hoisted up this idea of doubt.
Or, perhaps, it was just the canard of a new know-nothingism, but I find it hard to take talk of unintended consequences seriously.