I don't believe in Capital Punishment. Why destroy human life, we should preserve what we have. If someone causes an awful crime of course we want revenge but knowing that he was euthanized or whatever would honestly not make me feel better. Beating the stuff out of him/her might though. It would not change what already has happened and it would just be murder. You may say why preserve "bad" humans such as Adolf Riddler if say he did not commit Self Delete. Well I'm sure there's worse people than Adolf Riddler in our world and they just don't have the power to cause the harm he did.
Also Capital Punishment goes against our human rights. Everyone has the right to live according to the constitution.