THERE'S nothing quite so annoying as advice from the pious.

A friend of mine was once cowed into silence after mentioning to some mates that she was trying to conceive, thus, inadvertently unleashing a competition as to whose pre-pregnancy lifestyle had been the most blameless. First, she ventured that she had cut down on alcohol as well as caffeine. "You're still drinking?" exclaimed one woman. Another declared she had cut out alcohol and caffeine entirely and also avoided meat products.

My friend – who suspected the odd drink would make little difference, and that meat was a good source of protein – kept her unorthodox views to herself. They didn't seem to be the point. This was only partly a conversation about fertility; it was mainly about her friends jostling to show how well-informed and responsible they were.

It's an example of what the American journalist Katie Roiphe would call our tedious modern obsession with "wholesomeness". Being healthy, sensible, risk-averse: these have become the conventional values by which we judge ourselves and each other, as Roiphe sees it. In her new book, In Praise Of Messy Lives, Roiphe bemoans the current obsession with self-control, healthy living and protecting one's children. In this carefully calibrated environment, the sort of woman who quaffs the occasional glass of red wine while trying to get pregnant is falling short.

A divorced mother-of-two with a complicated relationship history, Roiphe terms herself "a failed conventional person" and is fed up of her purse-lipped judgmental contemporaries whose lives have always run along the tramlines of convention. Her life, by contrast, has been what she describes as "messy" – and she's sick of apologising for it. She challenges what she sees as her peers' tightly-controlled, conformist view of what is – and what is not – an acceptable way to live one's life.

She has a point. The expectation, alongside career, to marry, have children and move to a bigger house, appears to be as strong in some quarters as it was in the 1950s. Is there anything wrong with that? Not in itself, perhaps, but it can become a problem if those who haven't married or had children, or have divorced, or simply wish to stay put in the flat they bought in their 20s rather than move to a village, end up feeling as if they are somehow not measuring up.

Roiphe suggests that "mess" – both psychological and physical – is "a good thing, a lost and interesting way of life". If your love life is far from "sorted", if you drink too much on occasion, is that really so bad? And if your relationship breaks up, at least you then have the chance to "reinvent yourself". Most importantly, however, she challenges the tyranny of the conventional.

Roiphe is, of course, defending her own life but the spectre of crushing middle-class conformity and the minute ways people judge one another – from what sort of organic chocolate they buy to how many instruments their children play to whether they have "kept up" in the house-buying stakes – will be familiar to many. An obsession with perfect parenting (another of Roiphe's bugbears) is merely the latest manifestation of this hoary old problem. Many of us probably fall prey to such values without even realising it.

Where has it all come from? Most of us probably thought this was the blight of our parents' or even grandparents' generation. It could be down to the influence of television, but it's probably just that we humans can't help finding ways of establishing a pecking order while also defining what is right and normal, and therefore by implication, what is not.

The problem is that the apparently benign triumph of the conventional leaves little room for the unorthodox, the offbeat or Roiphe's "mess". The woman who reaches a significant birthday unmarried or divorced, the parent who would rather conduct her own extra curricular activity after work than taxi her child to yet another of his, the couple who don't want to marry, move to the burbs or give up their wine club subscription: a set of values that leaves such people feeling judged and excluded is far less "wholesome" than it might seem.