(Part 1 here). The other thing my Leave-voting friend said (echoing things I’ve heard in conversation from others) was this:
“Secondly, if migration is a right and A Good Thing, then logically population will flow to the 1st world cities and eventually you will have a few incredibly densely populated conurbations and the rest of the world largely abandoned. Is that a good outcome? Many countries – the UK for one – constructed policies to prevent that happening within their states because most people felt it was not.”
I can see where this concern comes from, but as stated I think it’s a kind of ‘spherical-cow physics‘: if you simplify your model enough, with a single metric of desirability and people’s choices explained simply by desirability, then the logical result will be everyone living in a few super-cities (which, for the record, I don’t think is a good outcome). But such simplified models aren’t really useful, for various reasons:
- People vary in what’s desirable to them (hence lots of people either never move to big cities, or actively move away from them);
- People have lots of reasons not to move, like attachment to home, family, culture, etc.;
- There are feedback effects (a destination can become less attractive if it’s too densely populated);
- Things other than migration affect population, like birth and death rates (if one area has much higher fertility than another, migration from the first to the second would stabilise populations, not concentrate them);
- Timescale matters – a problem in ten years is one thing, a problem in a hundred years is i) probably beyond our ability to affect, and ii) may well not happen just because some other parameter will change drastically in the intervening period.
But it’s a bit unfair to harp on issues like these. I suspect the point isn’t really about mathematical modelling, but more a sort of test of what sort of disagreement we’re having: are supporters of free movement so fanatical that they’ll say ‘yeah, even if it would lead to dystopian overcrowding in London, I’d still oppose deportations etc.’? Or will they instead say ‘no, if that was the foreseeable result I’d support border controls, but that’s not what will happen’? If the former, I come across like a crazy zealot; if the latter, I seem to have conceded the principle and the disagreement is just empirical.
And it’s not like overdemand for housing, infrstructure, etc. resulting from sudden rushes of people to the same big city isn’t a real issue – that kind of ‘overcrowding’ has been a big thing, for instance, at least since the industrial revolution (though my understanding is that it’s debated how much this was about the carrot of jobs and how much about active stick-type efforts to drive peasants off the land). Sometimes people arrive faster than housing, transport, and other sorts of infrastructure is expanded, and that’s a problem.
But I still think the choice which my friend’s argument tries to push onto supporters of free movement is sort of a false one. Mismatches between where people are moving and the infrastructure to support them can be addressed in a variety of ways – coercive intervention, subtler forms of incentive-manipulating (e.g. policies to encourage jobs or people to go to places more able to accommodate them), greater investment in infrastructure, etc. Saying that coercion isn’t a legitimate tool isn’t saying you can’t do anything at all.
(To use the reproductive analogy I like to return to, sudden changes in people’s reproductive habits can also be disruptive to public services etc., and that warrants political effort to solve those problems. But coercing individuals into having kids, or into not having kids, isn’t a legitimate tool for that political effort.)
Moreover, border controls arguably cause more severe overcrowding than they prevent – they just push it into refugee camps, detention centres, and developing countries that happen to border war zones. My friend’s question suggests abstracting from here-and-now to consider hypothetical long-term outcomes, but the problems worried about are already happening, in part because of the policies the question seeks to justify.