and this is precisely what the underdeveloped me of years past would have said as well.
My life experience has been the opposite. When I was in my 20’s and even my early 30’s, I very likely would have agreed with you; I probably would have even argued against the death penalty when I was a young adult. The older I get, the more I realize that some human beings are just pure trash, and they should be treated as such. Everyone should be afforded human rights, and everyone should be treated with kindness and respect, until the point that their actions cause harm to others.
As part of your own personal development, I hope that at some point you learn to take off the rose-colored glasses that you use to look at humanity and realize that while the world can be a beautiful place, it can also be a cesspool, and that punishing the people who actively try to make the world into a cesspool is simply the right thing to do.