Preserving the four-class system requires penal sanctions, even death.

Evidence

That without penal sanction the ideal of chaturvarnya cannot be realised is proved by the story in the Ramayana of Rama killing Shambuka. Some people seem to blame Rama because he wantonly and without reason killed Shambuka. But to blame Rama for killing Shambuka is to misunderstand the whole situation. Ram Raj was a raj based on chaturvarnya. As a king, Rama was bound to maintain chaturvarnya. It was his duty therefore to kill Shambuka, the Shudra who had transgressed his class and wanted to be a Brahmin. This is the reason why Rama killed Shambuka. But this also shows that penal sanction is necessary for the maintenance of chaturvarnya. Not only penal sanction is necessary, but the penalty of death is necessary. That is why Rama did not inflict on Shambuka a lesser punishment. That is why the Manusmriti97 prescribes such heavy sentences as cutting off the tongue, or pouring of molten lead in the ears, of the Shudra who recites or hears the Veda. The supporters of chaturvarnya must give an assurance that they could successfully classify men, and that they could induce modern society in the twentieth century to re-forge the penal sanctions of the Manusmriti. — Ambedkar, B R, Annihilation of Caste_ The Annotated…, 920