> is it desirable to use the fewest 'animal products'
It's not even a consideration. It is desirable to use the product which best
produces the desired result.
> is it possible for some people to be healthy vegetarians
No, IMHO
> is it possible for all people to be healthy vegetarians
Unequivocally NO
> what's the difference between a dog and a cow
For starters, the dog is a carnivore and the cow is a herbivore.
So what's your point?