<<Why should anyone respect the dignity of human life if even the state shows no such respect?>>
Because "human life" is just an abstract concept. In the real world, there is no such thing as "human life," there are only the lives of 300,000,000 individual human beings, all or most of them worthy of dignity and protection, and then there are the lives of some real low-life scum. When you've been duly convicted and sentenced to death, the presumption of respect for the dignity of your life is by definition abrogated. You're an exception to the general rule that human life is worthy of dignity or more accurately is not to be taken by human hands. The world is gonna be a better place without you. Nobody is going to have to clothe, feed and house you for the rest of your natural life. Nobody is going to have to live in fear that maybe one day you'll escape, or maybe one day you'll get your hands on a prison nurse or fellow convict. Your chances to do harm are all used up and the rest of us will breathe easier when you're gone. [Sure hope it's clear from this that "you" means the convicted criminal, not YOU personally.]
Now having said all that, I have to add that most of the worst criminals are products of a defective society and there's a certain unfairness in that we as a society have failed this person, yet it is he and not we that is going to pay for it. So I am in favour of using the death penalty maybe a little more sparingly, reserving it for the most vicious and sadistic of killers, the kind of guys that, no matter how much society may have failed them, they are a fucking menace and beyond all hope of redemption. The Talmud had a great saying that a court which imposed a sentence of death more than once in seventy years was a court of murderers. Meaning that only the exceptional case (once in a man's lifetime) would deserve the death penalty.