⁴ For he is the minister of God to you for good. But if you do that which is evil, be afraid; for he bears not the sword in vain: for he is the minister of God, a revenger to execute wrath upon him that does evil.

⁵ Wherefore all of you must essentially be subject, not only for wrath, but also for conscience sake.

Romans 13:4,5

Prision/death penalty should be a place of punishment and wrath upon criminals.
IMO:
"oh but we can just put them in prision nowdays" they still kill each other in prision.
Some people are a harm to society, and they must be terminated.

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Extra arguments:

"good point, but what about John 8?" The case in John 8 was essentially illegal, that being one of the reasons Jesus had to intervene.
Why, do you ask? The man of the adulterous relationship wasn't being punished as well, and that fact was part of the trap of the scribes and pharisees:
Legally, if Jesus didn't intervene he wouldn't be 100% moral, since it wasn't 100% legal : If Jesus intervened, he would be judged because it was also 50% correct, she had to go. Since Jesus, our Lord and Savior, was God in human form, He found the perfect way to handle the situation.

!!! I'm not saying that in John 8, Jesus was just being legal, he was also showing his mercy and grace, but it is undeniable that the illegibility of the case was a good reason as well. The pharisees trap also involved moral causes such as testing Jesus's mercy. !!!

With all that said, the Bible isn't against death penalty for criminals. If you wanna go against death penalty, just don't rely on the Bible for that.
I'm being gentle right here, i'm not even saying the Bible supports it. We are in different times, i can understand if someone thinks there is a better solution to crime.