It has nothing to do with Religion, that's the glory of the seperation of church and state, is that citizens of liberal societies actually enact that seperation in their daily life. Note for example welfare, which seems to be highly Christian, is ardently opposed by most Christian members of society because that is the place of an Christian individual and not the government. Locke wrote in his Second Treatise on Government that the death penalty is necessary in the situation of a Liberal government founded on a social contract, because the death penalty is the ultimate demonstration of the power instilled in the state by that social contract, and it is for this reason that we gave up our natural right to everything. Thus the death penalty is the ultimate proof of the power of the state, and should affirm us in our belief that we have done the right thing by joining the state, as the state enacts harsh punishments against those who would seek to take away the rights guarenteed to us by our social contract.

Of course Foucault would disagree, and say that this is the greatest example of the insecurity of the masses, and the highest act of the insecure Christian, as he needs to kill or imprison all of those who do not act in a Christian manner, in order to ensure that they are "normal." Who's right . . . well I can't decide that for you.