Its like many things in life - its to do with risk
There were more dogs that DID die prematurely in the past, due to illness, poisoning, exposure and sometimes farm/working dogs were shot if they developed arthritis, or became agressive
Similarly, the level of infant death was higher in previous generations; and babies born prematurely, or with special needs, often didn't survive
I agree things can be taken too far; I have to admit our house is nowhere close to sterile (and I let Molo lick my face, and he has been known to lick my daughters face too
), but I do think that if fewer children and pets die as a result of improved knowledge about their biology/psychology, then its a good thing