I am more concerned with capital punishment in my statements, not torture. That’s a separate issue.
The right to life is not inherent in man’s mere existence, but rather, it derives from his moral goal. Man’s worth derives from his ordination to values that transcend temporal life, and this goal is built into his spirit inasmuch as it is an image of God. Although the goal (Heaven) is absolute and the image indelible, man’s freedom means that by a fault he can descend from that dignity and turn aside from his goal. The philosophical justification for penal law is precisely an axiological diminution, or shrinking in worth, on the part of a person who violates the moral order and who, by his fault, arouses society to some coercive action designed to repair the disorder. Those who base the imposition of penalties merely on the damage done to society, deprive penal law of any ethical character and turn it into a set of precautions against those who harm society, irrespective of whether they are acting freely or compulsively, rationally or irrationally. In the Catholic view, the penal system exists to ensure that the crime by which the delinquent has sought some satisfaction or other in defiance of the moral law, is punished by some corresponding diminution of well-being, enjoyment, or satisfaction. Without this moral retaliation, a punishment is merely a utilitarian reaction which indeed neglects the dignity of man and reduces justice to a purely materialistic level.
Human dignity is something built into the natural structure of rational creatures but which is elicited and made conscious by the activity of a good or bad will, and which increases or decreases within that order of being.
We need to be careful about equating “dignity” which we can fall from and “image” which is indelible. One is worth, the other is nature. When you say “violating that dignity is not merely an offense against that individual [but against God]” you run into a problem with concepts such as self-defense. If a victim is being unjustly attacked and their life endangered, he would be violating “the dignity of man” by killing his attacker in self-defense. Not so, because the attacker, in choosing to unjustly attack, has descended from his dignity as a human. You also run into the confusion of equating offenses against man with offenses against God because you are equating their dignities. The next step is to equate their natures, and then we run into pan-theism. God is infinitely worthy, man is not. People are not gods, and they do not have God’s nature. An offense against human dignity is not an offense against God’s dignity (worth).
Maybe a better way for me to phrase it is how we “descend” from that dignity rather than say we “forfeit” it. However, when we are talking about capital punishment, where a person can be justly executed for grievous wrongs, we are talking about serious falls from “dignity”.