It would be churlish at Easter to point out that a religion prizing a mother's virginity might have a tendency to over-idealise the role. But I'm a churlish person, and it's not as if I asked the Right Rev Michael Langrish, Bishop of Exeter, to choose this time to suggest that the coalition is unfairly penalising what the Daily Telegraph calls "full-time" mothers. (Full-time! As if one is mysteriously de-mothered the moment one's child drifts beyond one's field of vision.)

Certainly, the coalition is unfairly penalising all sorts of people, particularly the poor and the disabled (who, by amazing coincidence, often fit into both categories). And it does appear to be penalising single-earner families, too. An Organisation for Economic Co-operation and Development (OECD) study found this week that the average UK family with one worker and two children lost 27.9% of their wages in tax in 2012, compared with 26.2% before the coalition was elected. This is now significantly above the international average.

Meanwhile, single people and two-earner couples have seen their tax bills fall since 2009, due mainly to rises in the tax-free personal allowance. Clearly, this increased tax burden on families puts primary carers under yet more financial pressure to return to work as quickly as they can. So this wasn't a good time for the coalition to have decreased financial help with childcare for parents returning to work either.

As the bishop points out, this is a bit rich coming from the Conservatives. After all, they moaned and complained right through the last Labour government that traditional nuclear families should be nurtured and rewarded, with marriage made attractive through tax breaks and single parenthood made less attractive through the removal of such luxurious fripperies as preferential access to social housing. He's especially disappointed that marital tax breaks have not materialised. Yet that, of course, would only alleviate financial pressure on those families that the church considers to have toed their own moral line.

To be fair, the bishop takes care to sing the praises of stay-at-home fathers as well as mothers: "Where one parent makes a conscious decision to stay at home for the children … they shouldn't be penalised. The evidence is that what the parent is doing is investing in a child's development, which can save the state significant amounts of money at a later stage. It helps children to develop into adults who are more likely to fulfil their potential and make a net contribution to society."

The trouble, of course, is that the penalisation of stay-at-home parents, still usually mothers, is nothing new. And it is not merely financial. It's all very well to make romantic speeches about the important work of raising a family. But historically and culturally, those who accept the traditional role of economically dependent spouse and parent become vastly more vulnerable themselves. That's precisely why, on his Thursday radio phone-in this week, deputy prime minister Nick Clegg felt the need to describe stay-at-home parents as having made a "noble decision".

In the past, when acquiescence to such a role was absolutely expected and demanded of women, they were hardly thanked for it. On the contrary, women's financial assets became the property of their husbands; their bodies were their spouses' to hurt and violate if they wished to; they were considered to have no role to play in democratic politics, and giving them an education was not considered worthwhile, since it would be "wasted" on bringing up children (which, far from being the most important thing a human could do, was at that time considered to be work for the ignorant).

People forget that in the UK all this outrageous and cruel discrimination only became unacceptable pretty recently. Remaining inequalities, such as the gender pay gap, attest to the fact that stay-at-home parenthood is still routinely punished, in the financial sense. This latest turn of the tax screw is a small regressive step in a situation that is much less regressive than it used to be, but is still regressive. In countries where women are less "liberated", but are supposedly revered within the household, the pattern whereby respect for motherhood comes at a very high price can still be plainly seen. All over the world, women with children are the poorest of the poor. Here, even a few years away from a career caring for children can hugely damage opportunities for advancement and success.

While politicians – and bishops – pontificate about the nobility of dedicated parenthood, there needs to be more understanding of the reasons why this sort of complacent idealisation isn't helpful. We hear much about the "guilt" working parents are supposed to feel. They feel guilty that they are giving their all to neither work nor family. No matter how gender-neutral the language, it is always the female half of a working couple who is expected to be suffering this guilt.

But perhaps most corrosive of all in this subtle game of Make Mums Feel Guilty, the paragons – the stay-at-home mothers – often feel guilty, too. I've talked to mothers who have been embarrassed to admit that they don't work. That's pretty awful. The received idea is that feminist harridans attack "traditional" mums and make them feel bad. The reality is that "stay-at-home mums" sometimes feel insecure precisely because they are uncomfortably dependent on their partners and worry about the challenge of regaining some autonomy in the future. And not without cause. Even if they are perfectly happy with their choice, women still feel that their own satisfaction can be – and is – used as a stick to beat other women who may not fit this prescriptive female archetype.

In truth, no matter how much it is fetishised by the likes of the Bishop of Exeter, women often find that being a "full-time mother" is tough. It can promote feelings of lack of identity or of self-worth, sometimes depression, undermining the very role that has been so nobly undertaken. This was as true back in the halcyon days of his childhood that the bishop harks back to – when it was far less common for mothers to work – as it is today. If full-time parenthood was as completely and unfailingly fulfilling as its cheerleaders suggest, then men would have been falling over themselves through the ages to try it out.

There's no need for this divisive debate. All parents need societal support, whether they stay at home or go out to work. All parents, whether or not they are "the breadwinner", need to understand that they are just as responsible for the emotional and educational welfare of their children as the other. Any singling out of a particular parenting style as "ideal" is undermining. Good parents, like medium parents and bad parents, are what they are, 24 hours a day, whether they are constantly by their child's side or not.

The underlying truth is that mothers are always expected to sacrifice themselves for the benefit of their families. It is, of course, iniquitous that the tax system discriminates against single-earner families. But that's not because it penalises "full-time mothers". It's because it penalises all of the adults and all of the children in those families. I wish this simple fact was a little more obvious to people than it seems to be.

• This article was amended on 1 April 2013. The original referred to cuts in the tax-free personal allowance. That has been corrected to rises.