So, you're arguing that a State has the right to legalize murder. That if North Dakota wants to, they can legalize stabbing to death. That's insane.
That's central to idea of a Republic that there are different local laws.
What is central to the American Republic is that we all have a God-given right to Life, Liberty and Private Property, and that our government officers, at every level, have a sworn duty to protect those rights.
Again, your argument removes any need for an American republic or a Constitution.
Yes. At one time it was legal to buy and sell slaves in the US. Someone here once said it was legal to kill a Mormon in Missouri. But that's the nature of a republic, the states are free to make their own laws. The price of freedom is failure. The alternative is central control. And what happens when the central government gets out of control is tyranny.
But I think it would be wise to have a Constitutional amendment to expel states if a state were to become so corrupt that they would legalize murder.