I don't support the death penalty. I mean yes, there are many horrible people out there who have done horrible things, and I have sometimes felt like death would be a justified punishment.
However, if I think about it for longer, I think life in prison can be just as bad as death. You are cut off from society and stripped of your freedom. In a way, I feel like that is similar to dying. (at least in the ways that matter to me)
I've also noticed that a lot of people like to argue that the death sentence stops people from committing crimes more efficiently than life in prison. However, if I remember correctly, the data shows that this isn't true. I think the crime rates aren't actually any lower in countries with the death penalty than those without. A lot of crimes are also not that carefully thought out and are more of the "heat of the moment" type. In those situations, the criminal won't think of consequences.
The main reason I don't support a death penalty is, that it is irreversible. You kill the criminal, and that's it. No takebacks. Not even if new evidence comes to light that proves the person who was executed was actually innocent. This has happened before, still happens and I doubt that it would stop happening, especially if even more countries started using the death penalty. (I think there have also been studies that show that these "wrong" executions unproportionately affect marginalized communities)