None of us know how many fathers will be there come Christmas morning in the Winslet-Rocknroll household - although one would most likely assume as least one, the dad of Kate Winslet's newborn baby boy, Ned Rocknroll himself.

Perhaps she is all set to have a grand gathering of the clans now linked through her children by three different dads. But we don't know (and it's none of our business). And nor does Fathers4Justice, despite the poster it has created using Winslet's image and the caption, "Kate, every child deserves their father this Christmas". Winslet has threatened to sue. And quite right too - though arguably she might have been better ignoring the whole thing and not giving the campaign the oxygen of publicity.

As an opportunistic abusing of a celebrity's words, this is pretty low. The advert was sparked by a loose statement Winslet made about parenting arrangements in a Vogue magazine interview, when she said of her children: "They've always been with me. They don't go from pillar to post; they're not flown here and there with nannies ... none of this 50/50 time with the mums and dads - my children live with me; that is it. That is it!"

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When the article first appeared last October, one Guardian writer suggested this was the kind of quote that, "if you're not careful will land you a guy in a Spiderman suit with a Fathers4Justice placard on your doorstep". And bingo, a couple of months later, Winslet almost becomes the placard itself.

Perhaps the reaction was inevitable. Women can't make statements about the way they conduct their family lives without having them criticised by some group or another - and Winslet gets her fair share of it. Earlier in the year, she was being slammed in The Telegraph for following in Ulrika Jonsson's footsteps in having a different dad for each baby. Zoe Margolis, writing in Jezebel, described this, rather graphically, as "slut-shaming".

Meanwhile, Fathers4Justice has probably done more to undermine its credibility with this than any other of its madcap stunts. Sam Mendes, Winslet's ex-husband, and father of her nine-year-old son, described it as "inappropriate" and said that the issue of fathers' rights "has never been a concern for me or my son".

It is not hard to see why Fathers4Justice often targets Christmas. 'Tis the season to get all misty-eyed and wistful about nuclear family life. It might have been better off, this year, choosing the case of a man actually denied contact with his children - though that would have got it little publicity. As it is, its current message - reacting to a brief Winslet quote dismissing 50/50 parenting - is rather muddled. Is it trying to make a point about shared parenting? Or about Christmas? Or is it just desperate for any kind of attention?

Besides, Winslet didn't say shared parenting could never work for anyone - just that it wasn't for her. And, to be fair, there is evidence to back this. For all that 50/50 is an aspiration, research suggests that it's not always best for children. Practically, the two-home, divided life, isn't always ideal, particularly when your parents are internationally separated.

We don't really have accurate statistics for how many children experience a fatherless Christmas - though Fathers4Justice says that "nearly four million children will wake up without a father this Christmas, often as a result of outdated and prejudiced views which treat a nation of first-class fathers as second-rate parents".

Again, this seems manipulative, a figure based on the 3.8 million lone parent households in the UK, 92% of which are headed by women. It doesn't equate to actual absence on Christmas Day, or indeed fathers being prevented, by evil, excluding mums, from coming down the chimney. According to the Economic and Social Research Council's Modern Fatherhood project, 61% of separated fathers describe their relationship with their kids as "very close" and 27% as "quite close".

The result come Christmas Day is, for the most part, not a "fatherless" Christmas, but a rather complicated one. What I've seen of how Christmas is navigated by post-break-up and single-parent families has been admirable.

For all that parents crave their children's company on that special day, people seem to come waving white flags, attempting to share time in a way that keeps the kids happy. I see families gathering in their original home, dad back for Christmas Day, or even for the night before. I see a mum take the morning; dad taking lunch and the afternoon; new couples choosing not to be together so that their kids can be with their actual parents.

Until recently I had always leaned towards sympathising with fathers' rights groups. However, a report produced by Dr Kirsteen Mackay for Edinburgh University's Centre for Research on Families and Relationships earlier this year made me question the prevalent notion that fathers are the victims of a court system that favours mothers. In fact, the reverse seems to be the case. Dads are generally given the contact they desire, whether the kids want it or not - even where there is a background of domestic abuse in the relationship. In fact, on an official level, this culture believes in fathers. It believes in shared parenting.

That's not to say that dads always get the time they should with their kids; some fathers give up on their battle for access without ever going to court. Indeed, outside of court - in the world where many more decisions on parenting are made - the idea that children belong to their mothers endures in an almost primal way. That's why Winslet's words were jumped upon - because she used the phrase "my children". But what else could she have used?

My sympathies go to those fathers who long to be with their children this Christmas but won't be - whether because they got New Year this time round, lost the connection with their kids years ago, or have been in some way excluded. I also feel for those children who are yearning for absent dads - or mums, or even grandparents. But this recent advert undermines any sympathy I have for Fathers4Justice. It makes it seem as if the organisation is flinging dirt at all women. When you target one woman, on the basis of so little, that is how it comes across - as a random slur on a whole gender. And there's no justice in that.