I couldn't have said it better myself

I'm glad I have Hendrik Hertzberg to articulate the vague thoughts in my head:

"A criminal may deserve to die, may deserve even to die in terror and agony; but no civil servant deserves to be made to participate in the premeditated killing of a person who, however wicked, is on the day of execution a helpless and frightened human being."

("Comment: Sentenced," The New Yorker, May 15, 2006.) You may (and you should) read the entire essay on the New Yorker site.