
Think owners who habitually neuter their dogs before maturity just do not notice what effect it has on the overall conformation and of course you have no real way of knowing if your dogs ill health is caused by or the result of neutering.
On the other hand if you have had a dog neutered young and a dog left intact from puppy-hood to death then you will know the difference and you would not neuter except for reasons of health.
Vets on the other hand often do not own a dog at all or if they do they will be a neutered cross breed so on two counts they will be unable to understand what the dogs life may have been had it had the advantage of being left intact and well bred, there are exceptions of course.