I'm going to put a different spin on spay neutering early, before it became the norm there were stray dogs everywhere, everyone had a dog with pups, people would drown them, shoot them, throw them in the ditch in the country, shelters were gassing lots of dogs, personally I'd rather have dogs fixed early so less dogs are getting killed everyday because of irresponsible behavior out of the owners. This new thing of it's unhealthy to alter your dogs has me concerned that we are headed back to such things.
in countries where spay/neuter isn't common (such as all of Europe), they actually have less of a pet overpopulation problem than we have in the US. it's irresponsible owners who dump their animals and don't take care of them.
No one is saying that it is unhealthy to alter them. Just that it should be done after they are mature.