If you think my general wariness of giving the government the right to kill people it doesn't like isn't enough, the #Catholic church offers the simple, additional argument:

Dead people cannot repent, reconcile, and reform.

We should be like Christ, who worked to allow everyone the chance to find eternal life, and not like the Roman state, who excuted Him. We should remember to put the First Things, first.

His Justice should decide someone's eternal fate, not ours.

We are not God.