Fulfil your civic duty. Get married. Have children. That was the message from Miriam Cates, the increasingly prominent Conservative backbencher, to guests at a drink reception earlier this week. In what even her fiercest critics would have to concede was an impressively bold speech, Cates suggested that many of her female constituents want to work less and spend more time with their children. She claimed that politicians belonged to a class that had been protected by marriage and family, insulated from family breakdown to such a degree that they fail to realise how important it is.

Few politicians can ride out a Twitterstorm without some sort of retraction, and Cates is no exception. She has since penned a piece for Politics Home arguing that her comments had been misreported and taken out of context. Her objective, she says, was to stimulate discussion. To be fair to her, it worked.

The MP is right that declining fertility in the West should worry us all. In 1941, around 20 per cent of women reached their 30th birthday without having at least one child. Now, it’s more than half. In the 1960s, the average number of children per woman was 2.5; it’s 1.6 now. This declining generational size risks creating a demographic crisis in the years ahead, risking both the existing benefits system and the economy’s ability to grow.

She sought to answer why fewer young people are having children by pointing the finger at greater female workforce participation, contraception and gender equality. But Cates was quieter on the positive side of these developments – fewer unwanted pregnancies and fewer women trapped in the home when they would prefer to be in the office.

Far more investigation into why young people are having fewer children is needed

So what can be done? Cates criticises our tax system, which treats us as individuals not households (the irony should not be lost on us that separate taxation was at one time a feminist demand). Politicians and economists often suggest that we should tax the bad and subsidise the good. Yet anyone looking at the UK’s tax code would assume policymakers believe families with two parents – or those families where one parent works part-time or in the home bringing up children or looking after ageing parents – are a bad thing. A single person with no dependents earning £40,000 per year will pay the same amount of tax as a parent earning £40,000 supporting a partner and children, even though the singleton’s outgoings will be substantially lower.

A couple where both adults earn £12,570 a year will pay no income tax. But if one adult in a single-earner couple earns £25,140 or above, they will pay income tax around £2,500. Worse, when one earner within a couple reaches £50,000 per annum, child benefit is withdrawn.

Surprisingly, since the furore Cates has doubled down on her comments about the privatisation of family life over the last few generations. Apparently we should no longer view children as a luxury, ‘like buying a Porsche’, she says. Since children are integral to our societal and economic prosperity, ‘we’ – by which I presume she means ‘the government’ – should do all we can to encourage young people to have them. Here, the former biology teacher is on shakier ground.

Treating families fairly is one thing. But it won’t be enough to raise British fertility levels to the replacement rate of 2.1 children per woman. Far more investigation into why young people are having fewer children is needed. Although, even then is unlikely to feed into government policy, unless we think Viktor Orban’s Hungary – where IVF clinics have been nationalised and couples who promise to procreate handed generous loans – is desirable.

Could app-based dating be encouraging people to stay single for longer? Could sky-high childcare costs deter some couples from taking the plunge? One report has estimated that rises in the cost of housing between 1996 and 2014 may have led to 157,000 fewer children being born in that period alone.

Too many politicians are either scared to discuss marriage or talk only in platitudes. Provided the welfare of the children isn’t affected, it shouldn’t matter whether they are born into families where the parents aren’t married. Perhaps the census data released this week, which found the number of people who have never been in married or in a civil partnership has risen from 30 per cent to around 40 per cent since the start of this century, shouldn’t bother us, even if we consider the huge regional and ethnic variations.

Married parents are twice as likely to stay together as non-married parents. Far more single-parent households with children where the parent does not work are in poverty than in couples where one parent works full-time and the other part-time. The trouble is, people rightly oppose state interference in private family decisions.

Cates might be on the money when it comes to taxation. But beyond that, the government would be better off introducing sensible policies to cut the cost of living across the board – including deregulating the childcare sector and liberalising planning – than engaging in Atwoodian, pro-natalist policies.