Actually, that's the Ron Paul position.
Since the Constitution is silent on death camps, the federal government has no role in regulating them.
Since the states have rights reserved to them under the 10th amendment, it's up to the states to decide the legality of death camps.
That's Ron Paul's logic on abortion applied to death camps.
And actually, Roe v Wade left things wide open to allow precisely that. They never said that every biological human being is a “legal person” after birth. They left the “legal person” definition open to be defined by whoever will define it. The only thing they said definitely about who is a “legal person” is that it can’t be somebody before birth.
So presumably a state COULD allow death camps, slavery, rape-rooms, or anything else as long as that state first defined “legal personhood” to exclude those particular human beings intended as victims.
Which is exactly what Adolf Hitler did.