I responded to the following:
The underlying concept is that offenses against God are infinite because he is infinite. This idea developed during the medieval period, when Anselm reinterpreted Jesus' substitution as satisfying a debt of honor to God. Scholars commonly see this as the result of the medieval concept of justice, where the same offense is different depending upon whether it's against a serf, a lord, or the King. The concept is that the severity of the offense depends upon the dignity of the person offended. I believe this is contrary to Jesus' picture of God. There are other approaches to the atonement. My preference is a combination of Rom 6 and Jesus' statement in the words of institution that his death is a covenant sacrifice to establish the new covenant.
Of course eternal punishment isn't necessarily tied to one's theory of the atonement. People have believed in eternal punishment without necessarily holding the Anselmian theory of the atonement. Thus my objection to your argument isn't fatal to the idea of eternal suffering. The strongest argument for me is Biblical. The usual moral justification is that the person chooses alienation from God. See e.g. the second posting in this thread,
http://www.christianforums.com/t7795908/#post64770392.
I don't see any way to avoid eternal punishment without a seriously non-literal interpretation of Matthew. I'm prepared to do that. Few others in CF are.