"Marriage is one of the most important of all social institutions."This is because, along with the nuclear family it is associated with, it is the last, crippled, vestige of the original tribe and community in which human nature evolved, long before the advent of civilisation, but which, between them, state and a money, wholly for-profit economy have over the centuries (especially during the last) made redundant.
The state, which usurped our original tribes and now poses as our nation, which we mistakenly assume exists to serve us, was in fact created and has developed over the centuries to facilitate society's self-exploitation to the advantage, originally of just the rich and powerful, but nowadays of a very numerous and diverse elite, and, paradoxically, because of their role in modern democracy as clients and consumers to certain professions and capital interests, the "disadvantaged ".
The state does serve us, of course, and we all depend on it, but as a shepherd serves his flock, which is not primarily for the flock's sake (notwithstanding any genuine concern felt for a lost or injured lamb), but for his own and/or his employer's sake, for the meat and wool the flock provides and can be exchanged at market for money.
Why have our social scientists not recognised this fundamental truth? Because they, like the medieval clergy, belong to one of society's favoured elites (academia) and thus, instead of seeking a real understanding of society and its workings, are more concerned, subconsciously, with rationalising and justifying the socio-economic status quo on which their own privileged status depends.
This also explains academics' (and members of other privileged elites', especially in politics and the media) subservience to state ideology - formerly Christian, i.e church ideology, now the ideology of "colour-blindness", or One-Human-Racism", which denies, demonises and suppresses as "racist " the importance of race and ethnic origins for any deep and meaningful sense of personal and group (i.e. tribal or national) identity.