The other “scaling” problem comes in the difference between, on the one hand, a small percentage of people trying to make polyamory work where various combinations exist, and on the other, a society built around normative polygamy or polyandry with associated prestige for those with multiple partners. With the latter, and I’m specifically thinking of Fundamentalist Mormon groups, there is virtually no way to avoid a demographic crisis with various forms of authoritarian awfulness as your only social “band-aids” to keep the practice lurching along.