Critics of free immigration worry that immigrants might make the country more socialist, more crime ridden, more like the places they are coming from, but offer no strong reason to expect those particular effects. Leaving the place where you grew up to move somewhere very different is, after all, evidence that you prefer the latter. As I pointed out in one exchange, the Volokh brothers, associated with the popular libertarian/conservative legal blog the Volokh Conspiracy, are immigrants from the ex-Soviet Union. While Eugene and Sasha Volokh are slightly more socialist than I am, they are much less socialist than most of their fellow academics, not entirely surprising given that they have experienced socialism at first hand.

The same assumption, that change is presumptively bad, appears in arguments over global warming. It seems likely that the average temperature of the globe will go up by several degrees C over the next hundred years due mostly to increased carbon dioxide in the atmosphere. If I had to guess, my guess would be that the net effect of the change will be positive, for at least two reasons. The first is that human habitability is limited mostly by cold, not heat—the equator is populated, the poles are not. The second is that, for well understood reasons, global warming can be expected to increase temperatures more in cold places and at cold times than in warm. Combine those two and one might guess that a somewhat warmer world would be, on the whole, more suited to humans, not less. Yet most people discussing the issue take it for granted that the change is bad, indeed catastrophically bad. A similar pattern holds for a variety of other issues, from fracking to cloning to GMO foods.

I call it a mistake, but perhaps that is unfair. The present is at least tolerable, since we are at present tolerating it. A change might make things better, might make them worse, so why chance it? That sounds like a plausible argument, but it contains a hidden assumption—that stasis is an option, that if we do not have more immigration our cultural and political circumstances will remain the same, that without anthropogenic CO2, climate will stay what it currently is.

Both are demonstrably false. Over my lifetime the cultural and political institutions of the U.S. have changed for reasons that had little to do with immigration. Over the past million years, the climate of the earth has changed radically time after time for reasons that had nothing to do with anthropogenic CO2. A rise in sea level of a foot or two would create problems in some parts of the world, but not problems comparable to the effect of half a mile of ice over the present locations of Chicago and London.

The left wing version of the conservative mistake comes with its own pseudoscientific slogan, ‘the precautionary principle.’ It is the rule that no decision should be made unless one can be confident that it will not have substantial bad effects, that the lack of a reason to expect it have such effects is not enough. It sounds plausible, merely a matter of playing safe, but a moment’s thought should convince you that it is not merely wrong, it is internally incoherent. The decision to permit nuclear power could have substantial bad effects. The decision not to permit nuclear power could also have substantial bad effects. If one takes the precautionary principle seriously, one is obligated to neither permit nor forbid nuclear power and similarly with many other choices, including acting or not acting to prevent global warming.

Continuing with that example, I have long argued, only partly in jest, that the precautionary principle is a major source of global warming. Nuclear power is the one source of power that does not produce CO2 and can be expanded more or less without limit. A major factor restricting the growth of nuclear power has been the precautionary principle, even if not always under that name—hostility to permitting reactors to be built as long as there is any chance that anything could go wrong. That example demonstrates my more general point: Stasis is not an option. The world is going to change whether or not we permit nuclear power. There is no a priori reason to expect the changes if we permit it to be worse than those if we do not.

I am not arguing that there is never a good reason to fear change; sometimes a change can be reasonably predicted to have bad consequences. I am arguing that much opposition to change, across a wide range of different topics and disputes, is based on the mistaken assumption that if only that particular change is prevented, the next year, the next decade, the next century, will be more or less the same as the present.

That is very unlikely.