The death penalty is wrong because the universal right to life (even for the most evil) is the building block upon which all other rights are constructed or derived. The right to life is conserved not primarily for the benefit of the criminal, but for the benefit of the moral structure of society.
That New Mexico has abandoned the death penalty is to be welcomed, even if the state is acting for financial reasons rather than ones of principle.
This point should be made: every case of the death penalty is wrong, not fundamentally because it is expensive or that it fails to act as a deterrent, but because the right to life, even of the most evil, is a moral absolute, just as the right not to be tortured is – or at least in theory.
More precisely, the right to life is the building brick upon which other rights (e.g. the right to be treated with dignity) are built. Abolishing the death penalty does not of itself guarantee a civilised society, but it is not possible to have a civilised society in which people are sentenced to die.