I don't think there is any rational basis for any given morality. It's all culturally contingent or constructed and to be argued over
The above is an extreme form of cultural relevancy, and fortunately, it is rejected even by the vast majority of cultural anthropologists. One of my undergraduate professors told the class of his experience of working with a colleague to perform an ethnography of a certain culture. They discovered rank child abuse (very, very young girls). His colleague didn't want to report it to the government because he thought is 'was just their culture,' and he used SLB's argument above to justify his position.
Law are simply cultural mores that become have so well established that they are codified. Therefore, all laws stem from morality.
Hence, using SLB's logic, all laws are irrational, culturally contingent, and "to be argued over."
The flaw in his reasoning is to say that there is no "rational basis for any given morality." Of course there is a rational basis because societies as a whole function as rational groups who are seeking their best interest. That's why world-wide mores (e.g., rejection of murder) are the most rational of all.
The legal concept that the state must protect its assets, including its human assets (children), stems from a moral norm held by, as far as I know, all nations. It's held by all nations because it is in their rational best interest to do so.
The only issues that are argued are the ones we have discussed here: when, how, under what circumstances, etc., the state should intervene.
Edited to add: SLB's position can also justify the anarchist's actions, which is something my poor city (Seattle) is all too familiar with.
