Placenta burying is not exclusively Māori but part of a wide network of traditions shared between societies, presumably reflecting our common ancient origins. Lots of cultures do it. Lots don't. But he's right about the irony.
Pākehā have been burying placentas for decades. My first child's placenta was planted in our garden in 1983. (This was in Grey Lynn, it probably won't' surprise you to know.)
The word whenua means both placenta and land. Connecting your child's whenua with their home seems a fitting thing to do, as opposed to consigning it to a hospital incinerator to be destroyed along with other body parts that have been separated from their owners.
There's currently a vogue for eating them too, not just for symbolic reasons but in the belief, that this incurs numerous health benefits. There is absolutely no scientific evidence to support this.
However, one person's appropriation is another person's sharing. One of the beauties of New Zealand is the growing number of Māori traditions that have been taken up by Pākehā, often without anyone noticing.
Funerals are a good example. Not so long ago, open caskets were unusual, bodies were never returned to the family home before the funeral and one person might be shoulder tapped to say a few words at the service.
Now open caskets are the norm, it's customary for family to sleep in the same room as the deceased at home for a night or two before the service and we're all familiar with the feeling of dread as yet another person who barely knew the bloke stands up to share their memories of good old Stan.
More significant – and a fine example of Rankin's kind of irony - is the growth of interest in te reo Māori, perhaps the ultimate piece of Māori culture Pākehā tried to destroy.
Many Māori are now being generous in supporting Pākehā attempts to make te reo part of their lives, however ineptly.
These are still complex and subtle issues, as we saw in the recent debate over whether or not a Pākehā woman was entitled to have a facial moko. And there will be more slips and stumbles along the way, such as the fuss over Rangitoto College First XV's haka.
There will always be cases where the right to engage in practices has to be earned by individuals. But everyone gets a placenta.
It's thinking in terms of "us" and "them" that impedes progress, by emphasising difference. It's far better to think in terms of "both of us" so that we work together.
It's an attitude that is already making our country a better place to live in – and one into which we can be happy to welcome any child.