Humans have a soul, a conscience - whatever you want to call it, that sets us apart from every other species on earth.
Animals don't have the luxury of expressing their emotions nearly as much as humans do and in spite of this, they can never "consent." That's the big difference.
Quite a silly topic and I laughed when I read "A friend of mine brings up a good point with regard to the logic of this argument." - It's not logical at all, actually. Appears to me like it's more a case of stirring the pot.