This is exactly why I couldn't do debate. I couldn't drop my beliefs and argue something that is 180 degrees out of phase with who I am. That being said, o0ne of the arguments the pro-let the murderers live side uses is that it is ultimately more costly to put someone to death than to just have life sentences. Don't know the veracity of that claim, though.
People often say that, but it's incredibly educational to argue the other side. You'll understand the side you support even better.