It's going to depend on the person. Peter Sutcliffe (The Yorkshire Ripper) wanted to be left to be able to starve to death at the end. Should these people's needs be catered to when they've done such heinous acts? Some criminals would prefer death.
Chris Watts who strangled his pregnant wife before smothering his two young daughters and dumping them in oil containers is haunted by the voice of one of his little girls saying 'no Daddy' as he brutally murdered her. I think he deserves to hear that the rest of his life.
So- in terms of the punishment functioning as a punishment, it depends upon the person.
Perhaps in principle, I might lean towards agreeing with capital punishment. It would certainly stop them reoffending! Rapists should be castrated I think. Might be more of a deterrent to those who contemplate doing it.
Big HOWEVER though! I don't actually support capital punishment. I think our justice systems are way too fallible. People have been wrongly convicted of both rape and murder. It's bad enough they end up doing jail time. We could hardly give them back their genitals or lives if they'd been taken away!
One thing I would like to see: If someone KNOWINGLY falsely accuses another of a crime and it's proven that they're innocent, the accuser should do the time for whatever they accused them of. It can massively damage a person's life to be falsely accused of rape or theft or, whatever. 'Victims' obviously need to be listened to, taken seriously and, the case thoroughly investigated but liars damage everyone.