— Derbyshire has a great encapsulation of the psycho-epistemology of conservatism. Derbyshire likes reason well enough, but wants to put it in its place. If we attempt to reason everything through to its logical end, we will, like Hume, find we can be sure of nothing. In practical affairs, we might find ourselves paralyzed if we attempt to justify each of our norms by means of reduction and analysis. Thus, as Hume says, “carelessness and inattention alone can afford us any remedy.”
Derb's problem is that when we think too hard about the institution of marriage, it's just plain hard to explain exactly why same sex couples shouldn't be allowed to marry. So the solution is to STOP THINKING and just carry on. He hopes that all our yammering on about our fundamental social institutions is like foundational questions of math. We don't know how to solve them, but it doesn't make that much difference to the math.
Now, it's not like there's nothing to this, despite the fact that Hume ran into his problem because of his bad epistemological assumption, not because reason is just like that. But we do rely on habituation, tacit knowledge, the internalization of norms, and so forth. And it is impossible to act well (if it is possible to act at all) if one attempts to justify all motivating reasons in advance of action.
But from time to time it's necessary to re-evaluate the norms we have endorsed and internalized. Why? Because the world changes. And our social practices, if they are worth having, are adapted to present circumstances. In general, we don't need to know what those circumstances are, or how our norms are fitting. We can just do our thing. But if it keeps coming up–if acting on a principle or according to a certain practice keeps causing problems for a good number of us–then we'll have to consider whether we want to just keep doing it this way.
If we decide that gays should be able to marry (and, yes, they should), then we can stop thinking about it again, and just go on living normal lives of carelessness and inattention. Granted, it is very uncomfortable to live through a period of revaluation. It throws things into doubt, and whatever we're doubting, it might be central to the way you conceive of your life, so you feel a bit shaken. And you don't know how to think about it, and you don't want to think about it. You just want to yell, “Stop! This is just how it is.” And that's fine, that's a natural reaction. But the issue keeps coming up for a reason. The reason is that “how it is” is flatly unacceptable to many members of society. And all they want is to change how it is FOR THEM, not so much for you. But during the revaluation, you're forced to suffer through the process of thinking too much, and because thinking is hard, the best you can do is justify the practice in the terms that are most familiar to you. And so you end up begging the question, because you assume that if its not exactly how it is, then it will be something fundamentally different, and everything will change.
But it won't. Everything won't change. Some things will change. And it will take some getting used to. Once you get used to it, though, you can just go forward, like number theorists who have only a passing recognition that the foundations had once been called into question.