Gen 9:5-6 NSRV
I'm sorry, but you took this passage way out of context. This was a warning for humans not to kill, for you may be killed as well. It is not authority from God to kill other humans. This quote comes into context if you also read the passage:
Jesus says: "You have heard that it was said, 'An eye for an eye and a tooth for a tooth.' But I say to you, Do not resist and evildoer. But if anyone strikes you on the right cheek, turn the other also; and if anyone wants to sue you and take your coat, give your cloak as well; and if anyone forces you to go one mile, go also the second mile. Give to everyone who begs from you, and do not refuse anyone who wants to borrow from you.
"You have heard that it was said, 'You shall love your neighbor and hate your enemy.' But I say to you, Love your enemies and pray for those who persecute you, so that you may be children of your Father in heaven;"
Mt 5:38-45 NSRV
Jesus was saying that revenge is a hateful act. The death penalty as a hateful act cannot be supported by scriptures in my opinion.
You may try to wiggle around it because it is an unpleasant thing but it is still the way He commanded. Let us look at Romans 13:3-5
For rulers hold no terror for those who do right, but for those who do wrong. Do you want to be free from 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.
Therefore, it is necessary to submit to the authorities, not only because of possible punishment but also because of conscience.
You are of course entitled to your opinion but Scripture does not support it. In fact it could even be argued that you are sinning by trying to evade your duty to revere human life by holding it valueless.
By abjuring the death penalty you are saying in effect that human life has no meaning and that murder should not be punished anymore harshly then theft or other lesser crimes. And yet Scripture says just the opposite.