It would only take one person innocently put to death to make the case the state is a murderer.
Yes, there are "innocent" people who are convicted and put to death... daily. Some governments are murderous. But a simple wrongful conviction and execution doesn't make the state a murderer. Rather, it makes the state fallible. Murder is the conscious, intentional killing of another for
no good reason. Capital punishment for a serious crime
is a good reason. We live in a fallen world, and even the most careful legal proceedings may be wrong at times, because they are influenced by fallen humans.
Romans 13:3-4 For rulers hold no terror for those who do right, but for those who do wrong. Do you want to be free from the fear of the one in authority? Then do what is right and he will commend you. For he is God's servant to do you good. But if you do wrong, be afraid, for
he does not bear the sword for nothing. He is God's servant, an agent of wrath to bring punishment on the wrongdoer.
A sword is a weapon for killing. This verse is reasonably clear that authorities are God-ordained to use deadly force. Does this mean that the force is only used appropriately? No, of course not, and many authorities who have misused it will answer to the One who gave it. Judgment Day will not be a happy time, but justice
will be done.
So what about the innocent one who is convicted in error, and not by malicious intent? His place is to trust in the Lord for eternal justice. He won't be disappointed. Anyone who brings about the conviction of an innocent person by malicious intent will probably answer to God as a murderer him- or herself. And any government which enacts unrighteous laws to make the innocent guilty will also answer to God.
Which would we rather have... a society where the danger of error exists side-by-side with the threat of death for serious crimes, or a society where even the most heinous crimes are treated lightly, and there is no fear of God as a result? I think given the fallen, sinful world we live in, the former would result in a more careful legal system, and overall a better society. But that's just my opinion.