1) We differentiate humans vs animals. If they're the same, then your reasoning either means we should all be vegitarians or it's okay to start slicing up death row victims and feeding them to others (oooh, maybe we can cut costs on prison food by feeding them to other prisoners)

Some states have assisted suicide now. So? Do people not have the right to die? But thats a whole other discussion.

Truthfully I'd have no problem either 1. Letting the families of the victims do what they wanted to the criminals or 2 throwing them into an arena ala ancient Rome and letting them fight to the death.

But, we don't do that. The criminal is treated humanely. They have human Rights. They have food, clean water. Clothes, TV. They have due process. In most cases (as you correctly pointed out) the case drags on for upwards of 20 years. They get appeal after appeal. That's more than their victims got.

2) One is sick and dying and presumably in pain. This last resort is to remove it's own suffering - and is done when there are no other options available. Or is that your go to move when your pet has the sniffles?

The criminal is a sick, twisted individual and we don't know how to fix them. For example you can't cure a pedophile. Therefore the last resort, yes, is to remove them from society. If you wanted to keep them alive to study them and see if by doing that we could gain insight into other killers and potentially stop them then that would be OK I guess, although then you're getting into the morality of that which would be a whole different moral question (is experimenting on people OK)

3) That you're comparing humans to animals, along with some of your other statements, is the barbaric viewpoint in and of itself. You believe there are human beings you can treat like animals.

We are animals. And again, some states are allowing assisted suicide/end of life decisions. Do people have the right to refuse chemotherapy if they want? Do the elderly have a right to decide to die?