If you’re too poor to have children, get a vasectomy. Better that than leave the nation “drowning in a vast sea of unemployed wasters that we pay to keep”. So wrote Ben Bradley six years ago, before he became a Conservative MP or a father himself, of Tory proposals to cap benefits for families. Just in case the meaning wasn’t quite clear, the keywords tagged for that blogpost included “chav” and “waster”.

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The party’s brand new vice-chairman for youth has of course now apologised for words written when he was only 22, plus an earlier post suggesting “police brutality should be encouraged” during the 2011 London riots. He insists he has matured. And while it’s a bold move for someone charged with winning over young people to portray youth as a period of dumb ignorance leading to professional embarrassment, let’s not nitpick here.

For argument’s sake, let’s assume that Ben has indeed grown up a bit. Let’s assume he now grasps not only how callous all this sounds, but how uncomfortable many find the idea of the state decreeing an “acceptable” family size, or punishing kids financially for choices made by their parents. Let’s assume he doesn’t secretly favour sterilising the unemployed to save everyone else a few quid, and probably never did; that he just got carried away on a blog nobody read, until BuzzFeed unearthed it.

But even then, the question remains: why do too many people on the right keep being caught out expressing such views? What to make of this seemingly visceral disgust at the idea of poor people breeding, which once manifested itself in myths about teenage mothers getting pregnant to get council flats – but, now that teenage pregnancies are at a record low, has clearly moved on?

What the affair doesn’t reveal is that Tories in general, or young Tories in particular, are somehow uniquely horrible. No party has a monopoly on juvenile idiots, as the homophobic drivel posted on chat forums by the Labour MP Jared O’Mara as a young man shows. All that’s changed is the internet making them easier to find.

But political movements do have individual strains of horribleness to which each is particularly vulnerable. For the Labour party currently, it’s antisemitism. And a strong contender on the right is this weird kneejerk fear of an underclass supposedly breeding like rabbits – while middle-class families confine themselves to one or two children – until eventually society is overrun with feral brats.

Sometimes it comes with a side helping of racism, and warnings about fertility rates for British-born mothers being lower than for those born overseas. It is perhaps especially attractive to the sort of men obsessed with taking back control over women’s bodies, given the juicy opportunities for berating selfish “career women” who don’t produce enough children, while lecturing their unemployed sisters for having too many.

Facebook Twitter Pinterest Toby Young ‘does share with some of Michael Gove’s circle an interest in how far IQ is heritable, and what that means for education’. Photograph: BBC

But essentially it is rooted in class prejudice. The grim unspoken assumption is that poorer people’s kids won’t be as bright or productive as middle-class children, and that these “wasters” (pace Bradley) will not only burden taxpayers but weaken society more generally.

This argument was skulking on the fringes of rightwing politics before Charles Murray wrote The Bell Curve. It’s what was so troubling about Toby Young’s long-forgotten article discussing whether, in the event of humans discovering a gene for intelligence, poorer parents should be offered a chance to raise their babies’ IQ through IVF by selecting genetically superior embryos. And it still surfaces periodically in US initiatives offering to pay drug addicts, prisoners or “welfare moms” to be sterilised. The root belief is that there’s something innately wrong with poor children, rather than with a system leaving so many in poverty.

For what it’s worth, I don’t think Young is a secret eugenicist. Someone who genuinely believed poor kids were biologically doomed could find easier ways of snuggling up to David Cameron than starting inner-city state schools. But he does share with some of Michael Gove’s circle an interest in how far IQ is heritable, and what that means for education.

It attracts some deeply suspect individuals seeking validation of the belief that the poor are poor because of some innate flaw

It’s a respectable enough area of research in itself, but on its fringes attracts some deeply suspect individuals, seeking validation of the belief that the poor are poor because of some innate flaw (and that everyone else is therefore off the hook). From that flows all too easily a conviction that this supposed flaw should be fixed before birth, or forcibly contained.

It’s a statement of the bleeding obvious that many Conservatives, even those who do believe strongly in individual responsibility, have no more truck with all this than many Corbynites have with demented conspiracy theories about Jews.

But enough rightwingers have flirted with these ideas to provide a bleak backdrop for any Conservative discussion about fertility and poverty. That’s why the idea of limiting benefits to two children and no more always left a nasty taste, no matter how much ministers insisted it was the fairest way of reducing the welfare bill for families, or was popular (which it was, among lower-earning voters who couldn’t afford big families and resented subsidising other people’s).

It wasn’t just the practical obstacles thrown up: what about multiple births, or pregnancies resulting from rape, or abusive men whose partners don’t dare deny them anything, or people unexpectedly losing their jobs after conceiving? What was troubling was the echo of a darker history, a sense that the right had forfeited its claim to the benefit of the doubt. It’s increasingly hard for a young man to leave his past behind. But as Ben Bradley has inadvertently reminded us, it’s infinitely harder for a political party to do so.

• Gaby Hinsliff is a Guardian columnist