So we have yet another example of the pathologising of child-free folk. Niall Ferguson, the historian and author, implied that John Maynard Keynes could not have really cared about future generations because he did not have children and was probably gay. Ferguson has apologised unreservedly, so fair enough, but it is interesting that the kerfuffle has mainly been about the apparent homophobia in the remark and not about the childless thing.

There is, among many otherwise intelligent individuals, an assumption that those of us who make a positive choice to not reproduce are selfish, rootless and have no concern about future generations or the planet. But those who have their own children often forget about the world and just worry about their own ever shrinking one.

I have seen the most passionately committed feminist activists go gaga once they give birth. All the promises such as "I'll still come on that march/go to that conference/burn down that sex shop" disappear when they sprog. All those in my circle with offspring seem to become unhealthily obsessed with their own little world. Principles go out of the window ("I still hate the private education system/healthcare but I am not putting my politics before my children"), and socialising becomes impossible. I even heard one of them utter that hideous phrase the other day – "We decided to go 'as a family'". As opposed to what? A circus act?

It is puzzling to me that child-free people are accused of being adults incapable of growing up and dealing with grownup problems. Have you seen the way some parents carry on, speaking to each other in baby voices and actually enjoying dragging themselves around the London Aquarium?

Yesterday I watched the film The Kids Are All Right again and wondered why I had a pang of longing (that lasted the same amount of time as filling my wine glass) for children of my own. And then it dawned on me that it was because one was leaving home for university and the other was so cute and trouble-free it would be like just having a stuffed toy to cuddle on occasion.

I have always been clear about children – some are fabulous once they grow into adults. This is where I am usually reminded that I was once a child, which of course is true, but I didn't like myself either until I could vote. I am proud to join the other child-free women, such as Oprah Winfrey, Dolly Parton, Helen Mirren, Stevie Nicks, Florence Nightingale, Georgia O'Keeffe and Dorothy Parker, all of whom have achieved rather a lot between them.

Having your own child is a selfish choice, as the world is overpopulated and there are millions of unwanted kids in institutions and on the streets. However, I have no problem with people wanting to reproduce, so long as they don't expect me to congratulate and thank them for saving the planet. My legacy – what I leave behind – will not be my DNA but my contribution to the emancipation of girls and women. So when people say to me, which they do with monotonous regularity, that they decided to have children in order that they could look after me and other child-free folk in our old age, I politely tell them I do not actually need them to do that for me. I would rather they helped change the world than add to it.