Short answer is yes. There are some people so inherently evil that their DNA needs to be removed from the gene pool, at least as a symbolic gesture. I say this as someone who has spent his life in support of progressive causes, including a tour as a public defender. There are plenty of safeguards in place to ensure that an innocent person is not put to death, and having the death penalty in place at least brings closure to victims' families.
I agree that it is not much of a deterrent, as people who would commit capital crimes are usually not sentient enough to understand the deterrent element in criminal sentencing.
Full disclosure: As the recent victim of brazen bicycle thievery, I am a little tough on crime these days, and I am tempted to urge that stealing bicycles from grouchy senior citizens should be added to the list of capital crimes. I'll leave that decision to my fellow seniors, though.
-- Eric Nordlof, Kennewick