But I think it's an aspect of my point; in conditions where you can rely on a steady stream of involuntary recruits in the form of foundlings, orphans, etc., avoiding this source of inter-personal tension probably helps make an island of collective organisation viable in a sea of individualism.
Of course, once the supply of orphans dries up, religious prejudices against sexual reproduction of the community become counter-productive. I believe the (very) few remaining Zoroastrians can tell a similar tale.
Julian