Experts say the hot debate, which was picked up by radio and TV during the week, is a symptom of the modern parenting environment.
Otago University senior lecturer in social work Emily Keddell said because parents were so emotionally invested in doing the best for their child, they were less likely to see their behaviour as a product of their circumstances and more likely to regard it simply as the "correct way" to parent. "It's much more loaded. You've got to get it right for the child you really love. You want to do well at it and you can't decide you're doing well at it unless you have some rules to measure yourself against."
She said many mothers felt a moral obligation to be able to prove they were selfless. Groups that shared their parenting approach would provide that reassurance.
She said some groups risked losing sight of the fact that babies are all different. "That is seldom factored into the rules they set for themselves."
There are New Zealand Facebook groups for whatever kind of mum you want to be: a "crunchy" natural mum, babywearing mums, young mums, working mums, farming mums, frugal mums, anxious mums, feminist mums and mums of babies with reflux. Some have several thousand members.
Baby-care consultant Jayne Eddington said groups sometimes formed a herd mentality.
"People who have lost their in-real-life community have found it on Facebook. They get emboldened by their community and come from a space of being 'right'. There's no 'your way works for you and that's okay'. The middle ground is lost."
Rochelle Gribble, editor of parenting website Kiwi Families, said parents joined online groups for support and a sense of identity.
"They'll say, 'I've found my parenting tribe'. There's sleep but there are other ones: babywearing, antivaccination, no sugar. Sometimes I feel quite surprised by the strength of people's commitment to these things."
