Rod, I think you can make your personal point about believing the growth plate/maturity argument without offending people by arguing they (have) put their dogs at risk (certainly no more so than by not neutering!). Even these studies indicate 'risks' are pretty darn tiny. And they are challenged by other studies. And in some the study group of dogs was TINY -- sometimes just 10 dogs. Not very statistically significant.
Overall, I feel those studies cited are misleading in how they are used as an argument against neutering. There are significant differences in actual likelihoods of any dog having any serious issues over a lifetime from neutering (that comparative study, if you delve into it, reveals tiny fractional increases on the con side of neutering for various problems, while the preventative protection of neutering is for diseases that have huge potential impact -- such as mammary tumours).
I strongly feel that in many ways the larger arguments for neutering are the behaviour/management issues (which can directly lead to increased deaths, greater than what is accounted for by health issues, I would wager) and welfare reasons. Ask any vet or anyone in rescue: there's a far greater death risk or abandonment risk to any dog left intact simply from the innate behaviours of intact dogs. Neutering generally prevents/resolves the potential behavioural problems that cause owners to abandon, put down, sell on or send to the pound, an intact dog. It also eliminates the primary cause of dogs roaming and/or escaping -- males roaming after females in heat, or females escaping while in heat to get to males -- the end story of which is often a dog lost forever or killed by a car or other accident. Typically these dogs are young, going through puberty/first heat. and owners cannot manage them, are ignorant of risks, or choose not to.
Having talked to many pound personnel over the years, they say they get dogs handed in for behaviours owners could have limited or ended simply by neutering. Most surrendered dogs in pounds worldwide can be pts immediately or within 24-48 hours. The reclaim rate for dogs is also very low at pounds worldwide. They also say they often bring in whole posses of dogs, consisting of one female in heat being assaulted by a crowd of fighting males. Around 90% of the male dogs in pounds here are unneutered males. Most of the females are not spayed. Very often they are in heat. Many of the behaviours are harder to manage if the dog is neutered (males ion particular) after they start eg at later than about 9-10 months.
If people are persuaded by the argument about growth plates they can simply wait to neuter til their dog is one-ish but by waiting two-three heats to spay a female, the lifetime risk of mammary tumours, half of which are malignant, rises to 25%.
As for NAIA. I cannot take seriously any argument from that lobby organisation that has led the drive to prevent any productive work being accomplished on puppy mills because they feel breeders never should be subject to any kind of inspection (not in any workable way). In the past I've seen them send out warnings to breeders in specific areas to indicate there may be a raid on those wonderful responsible breeders with over 100 dogs in breeding cages.
These often were passed around the old CKCS L-list. NAIA to me, are a breeder led lobby at the bottom of the barrel in having any right to moralise about dogs on any issue whatsoever. :x Oh, and that Mercola vet. The same one who recently chirped away about the things you need to adjust for with your flat-faced breeds, who have just a few little issues due to those flat faces people bought them for -- rather than taking the chance to discuss what you yourself have so well argued about the snub faces being a serious health risk and the flat face, which leads to eyeballs falling out of shallow skulls and serious breathing difficulties, maybe being a feature we should take a stance on for the dogs' sake.
In despair at a vet industry that just rubberstamps the status quo health issues most easily prevented by not breeding for such features, I sent that Mercola article on to a few researchers, who were pretty disappointed that vets like this cater to their clients and audience and do not take the initiative to highlight a far more serious issue than might ever be encountered in an early spay. And unsubscribed from their nerwsletter.