On communities, unwanted pregnancies and laws of large numbers
@Matthias and all, the Amish story points rather to the fact that communities do go for prevention, at least in some cases, and in a way that no health system does. @Lakomaa thinks this is because in modern care system, the entity receiving the care and the entity paying for it are always separate: sick person vs. taxpayer for state provision, insured-insurance company for private sector provision. So, it is always privately optimal to dump the cost of healing onto others, rather than assume the cost of prevention oneself.
Seen through this lens, community provision is fundamentally different, because the entity receiving the care is not an individual, but the (sub-Dunbar or equivalent) community, and that’s the same as the payer. Hence the apparent lack of market failure in care provision among the Amish.
So what’s going on with prevention of unwanted pregnancies? Public health people I have talked to tend to shrug and say it’s endemic. The window of opportunity for stupid and careless behaviour is a little too wide, the drive for instant gratification over prudence is literally a biological imperative, and even the best contraceptives only have a 99.99% effectiveness. If, say, in Italy you have about 20 million couples, if 10% of them are having sex tonight and all of them use contraception, you are going to get 200 unwanted pregnancies tonight, in just one European country. Best you can do is reduce the incidence of such incidents, but no human society ever achieved zero unwanted pregnancies.