Yes good point. I agree that the pundits’ anxiety attack over the “sex recession” and the contemporaneous (not necessarily causally related) reduced birth rate in affluent nations is, at heart, a caste/race/class anxiety. Or, to be less impersonal and diplomatically abstract, I think that white nationalists come in many flavours :-) and that many who are not overt skinheads still worry that non-Anglo persons are having more babies than Anglos.
[Of course, the environmental impact of each affluent Anglo baby is huge compared to the footprint of, say, the average kid born to a peasant farmer in Tamil Nadu. So it is actually quite appropriate for Anglos to have fewer kids at this point in history, because each (affluent) Anglo kid does way more environmental damage than his/her less privileged contemporaries. ]
This fear of being “overrun” haunts Anglo rhetoric. It was even, iirc, used by the English against the Irish (those damn Catholic Irish having as many babies as possible, overrunning our fine British cities blah blah); it’s important to remember that to several centuries of the ruling English, the Irish were what today we might call “non-White.” They were considered illiterate savages, racially as well as culturally inferior to any product of the Home Counties.
The same fear has been voiced many a time by Anglos looking anxiously towards Asia (cue familiar tropes about the “teeming hordes,” “Yellow Peril,” etc). Wherever people cling to race or ethnicity as a primary identification and loyalty-nexus, they seem to feel an pre-human, almost insect-like compulsion to outbreed the Other Guys. It’s interesting that this racial obsession doesn’t crop up as strongly in all imperial cultures; ancient Rome in its “high” imperial phase was, if not quite colour-blind, far more attentive to (and heartily ready to discriminate based on) citizenship, free vs slave status, aristocracy vs commonality, cultural literacy, wealth, formal religious practise and language skills than to shades of skin or hair growth types.
As far as I have gathered from (admittedly) non-scholarly reading, ancient Rome did not consider “ethnic groups” a problem so long as they became Romanised, that is, accepted Roman cultural norms and practises. The Anglo-American empire practises a distinctive insistence on trivial genomic variation as more important than acculturation or success, to the extent that many white Americans could not and still cannot stomach the idea of a dark-skinned President. Even a professional politician so very American, so urbane, well-educated, and qualified as Barack Obama was unacceptable to many white Americans not merely because of his party affiliation, but because of his skin colour.
Colour me cynical, but I do read White Panic between the lines of these alarmist essays on the “sex recession.” Not every line, of course. But there’s just a whiff around the edges. This racist panic also, as pointed out by Mark Sugg above, in turn colours (sorry, couldn’t resist) attitudes to women. An obsession with racial purity and “outbreeding” other races requires strict policing, and forcible impregnation, of the “right colour” of women; in mirror image, an excessive enthusiasm for eugenics leads to schemes for sterilisation or forcible abortion for women deemed likely to product “unfit” offspring. Nazi history leaps to mind of course, with the infamous Lebensborn programme. Seems to me that the Soviet state applied similar reasoning to a plan to “outbreed” the decadent West with a huge generation of well-indocrinated red-diaper babies. In their case there was more carrot than stick, with rewards and perks for “super proletarian mothers” who bore heroic numbers of kids for the Cause.
When women’s bodies become the contested terrain of political causes and schemes (causes other than “more freedom for women,” that is), the results are generally misogynist and downright nasty.