It seems like they should be able to slowly grow in size even if they are very inefficient, no?
Not really. Without some edge over other potential uses for that land, they'd eventually overstretch and collapse (if they loan to each other, even in hopeless cases), or reach an equilibrium where they're losing land to things like property taxes, probate, and adverse possession as fast as they're buying it up.
I can imagine a future scenario where Amish people own all arable land on Earth and everybody else lives in skyscrapers, arcologies, space stations, or some combination thereof. It seems weird, sure, but 1) I would take that as strong evidence that they're simply better at making use of arable land, since they'd still be selling food to everyone else and competing with e.g. terrain-independent hydroponics, and 2) they seem to have little or no interest in expanding beyond the agriculture and specialty-manufacturing industries, and that's the kind of thing where who does it isn't as important as how well it gets done.
Shortsightedness has a well-known tendency to lead to longterm losses, yes. This goes back to basic rationality: if someone else is doing what you claim to want to do, and doing it better than you are, you'd better either start doing it their way, or figure out what you really want.
I forgot about property-taxes and things.
I think that those are basically, pretty much, a way of us unfairly stealing their land.
However there are no ethical issues with it - so I think that makes sense.
As we become more awesome, property values + property taxes will rise until low-tech agriculture cannot compete.
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?