it is a deeply unsustainable situation.
It's deeply unsustainable in the sense that geometric population growth of any kind is unsustainable in the long run, yes. I don't know if it's unsustainable in the sense you seem to mean it.
Every community is in a sense free-riding off of other communities (public goods in general); no complete accounting exists for Kiryas Joel, although the last quarter of the NYT article is basically discussing whether Kiryas Joel is a drain or not, with no clear conclusion.
And the question strikes me as pretty much a distraction; if you don't like Kiryas Joel, one could look at more 'respectable' high-growth groups and ask the same Hansonian questions; the Amish and Mennonites come to mind as groups rarely criticized for being welfare queens and with high growth rates (sufficiently so that they keep spreading out and moving out of Pennsylvania to find farmland). Unfortunately, their rates are not so high as to be as dramatic as Kiryas Joel.
I find the second parenthetical statement deeply, viscerally terrifying. I'm going to tap out in terms of my personal rationality on this issue, but I would just like to ask all the interesting questions this raises:
Will significant human natural selection happen before the extinction of the human race? If it were to happen, would it be a very bad thing?
I was browsing my RSS feed, as one does, and came across a New York Times article, "A Village With the Numbers, Not the Image, of the Poorest Place", about the Satmar Hasidic Jews of Kiryas Joel (NY).
Their interest lies in their extraordinarily high birthrate & population growth, and their poverty - which are connected. From the article:
From Wikipedia:
Robin Hanson has argued that uploaded/emulated minds will establish a new Malthusian/Darwinian equilibrium in "IF UPLOADS COME FIRST: The crack of a future dawn" - an equilibrium in comparison to which our own economy will look like a delusive dreamtime of impossibly unfit and libertine behavior. The demographic transition will not last forever. But despite our own distaste for countless lives living at near-subsistence rather than our own extreme per-capita wealth (see the Repugnant Conclusion), those many lives will be happy ones (even amidst disaster).
So. Are the inhabitants of Kiryas Joel unhappy?