The position that punishment should be proportional to how serious the offense is but that repeat offenders should receive harsher punishments than first-time offenders is unsustainable  It implies that considerations as remote as what an offender did years ago are relevant to the seriousness of an offense  If such remote considerations were relevant, almost every other consideration would be too
But this would make determining the seriousness of an offense so difficult that it would be impossible to apply the proportionality principle
It is the overall conclusion in favor of which the argument offers evidence.