Only if you ignore obvious, original intent. And ignoring, obvious, original intent is a very bad precedent to set if we want to have our Constitutionally enumerated RKBA respected despite significant changes in firearm (and other weapon) technology.
The black letter language of the 5th amendment, adopted concurrently with the "cruel and unusual" prohibition in Amendment 8, clearly contemplates and permits capital punishment. To wit:
No person shall be held to answer for a capital....crime, unless on a presentment or indictment of a Grand Jury, ... nor shall any person be subject for the same offense to be twice put in jeopardy of life or limb; .... , nor be deprived of life, ...., without due process of law; ....
Unless the framers were so dense as to write one amendment in the bill of rights that clearly permits capital punishment (phrased 3 different ways) with proper due process while writing an outright prohibition on capital punishment in another amendment in that same bill of rights, we must conclude that original intent of the 8th amendment does not prohibit capital punishment.
Looked at in historic context, it is obvious that the prohibition on cruel and unusual punishments was directed not at mere capital punishment, but at deliberately tortuous acts such as drawing and quartering in which a live person was cut across the mid-section and then pulled to pieces by 4 draft horses (or some machine) tied to each of the four limbs, the iron maiden, and other methods intended to inflict maximum pain.
Interestingly,
this article at the Federalist Blog argues that the term has nothing to do with actual punishments imposed or how much pain they inflict, but is instead intended to prohibit extra-judicial penalties. Not sure I fully agree with that, but I present it for consideration.
To be clear, there are fine reasons a person may oppose capital punishment including personal "religious" beliefs (whether of a formal church, or simply personal morals), concerns about the state wielding such power, or the risk of imposing an irreversible penalty on an innocent man. I think, however, that it is clear there is not US federal Constitutional prohibition on capital punishment. Which, of course, has zero bearing on whether 5 SCOTUS justices will declare that the US federal Constitution prohibits capital punishment.
Charles
