"WE aren't taking God's place by imposing the death penalty. He's told us that we are to get rid of these vermin in Genesis 9:6
"
That may well be. However, my own ethics are not guided by the Old Testament. If yours are, then you're welcome to your opinion. As I said, this is my opinion. That's all it is. I don't insist that anyone share it.
Are you arguing that since Jesus preached forgiveness that no one on earth should be punished for their crimes in any way?
Then what of Romans 13:4 and Revelation 13:10?
"But if thou do that which is evil, be afraid; for [the state] beareth not the sword in vain: for he is the minister of God, a revenger to execute wrath upon him that doeth evil."
"... he that killeth with the sword must be killed with the sword..."