I do not love the idea of capital punishment. However, some people are beyond hope in this life time and could never be rehabilitated. Keeping them in prison for decade after decade is not going to do anything but cost the tax payer money. In cases like this I would understand the use of the death penalty to deter crime.
People who kill people for recreation shouldn't have a chance to live on this earth. People who think this way, aren't human anymore, they are past rehabilitation, and paying for them to live in prison for life is a burden on the taxpayers. Tax payers shouldn't have to pay for prisoners to live after committing such unthinkable crimes.