How is that different from arguing that it would be OK to eat a pig that was born deformed and killing it would put it out of it's suffering?
Depends what sort of deformity you're talking about?
As that parallel would point out, there would be cases where it is OK to eat meat.
I don't think any reputable vegan would say ALL forms of eating meat is wrong. If you're in a situation where the only way you can live is to consume an animal, then that's your right to survive. However most people in developed countries DO have a choice.
It's a stupid pointless argument, and it does nothing to shoot down the idea that intelligence is a key factor in why it may be OK to eat animals.
Well, it's covering the ground for people who believe intelligence is somehow a value of worth.
Mentally deficient humans are still human
Right, but strip away the human part and you're talking about an animal, we are just primates who have a few favorable genes and a unmatched frontal cortex.
and their well-being still matters to other humans that do have intelligence, and whose suffering would be increased by harming the mentally deficient human.
Could you make that argument for an animal though? Is ripping an infant cow away front its mother not increasing the suffering of the mother cow? The philosopher Jeremy Bentham once said "The question is not, Can they reason? nor, can they talk? but, Can they suffer?".
My question really is, you somewhat tacitly stated yourself, that the suffering of others (loved ones) is what is the moral downfall here. Why is it ok for a cow (animal) to suffer but no human (animal) to suffer? What is the line that you draw to separate them?
Besides that, we instinctively treat members of our own species with value, we don't eat them unless there is a very last resort....it really just makes no damn sense.
This isn't true though. Have you look through history? We have hung people in the streets, broken people limbs and left them to die, burned people alive, beheaded heretics, strung people on crosses. Specie has very little to do with it, we value people in our tribe, in our social circle. Human life means very little if you see someone as an enemy. Not to mention there are plenty of instances of cannibalism throughout history.