Idolatry vs. Physicality

The prophet Jeremiah speaks of two kinds of false prophets: 

In the prophets of Samaria I saw a repulsive thing: they prophesied by Baal and led My people Israel astray. And in the prophets of Jerusalem I saw something horrifying: adultery and false dealing. They encourage evildoers, so that no one turns back from their own wickedness. To Me they are all like Sodom and [all] its inhabitants like Gomorrah. (Jeremiah 23:13-14)

Which is worse? Those who prophesized in the name of idols or those who cheated and encouraged evil? 

Well, it seems pretty clear that the latter are worse. After all, the inhabitants of Samaria are still called "My people" though they have been swayed to idol-worship. However, the inhabitants of Jerusalem are compared to Sodom and Gomorrah, which is pretty bad. 

I'm not convinced this is what Lewis had in mind, but perhaps it helps us differentiate the reign of the White Witch versus the reign of the Telmar. There were Talking Beasts who joined the White Witch. They became the enemies of Aslan but never ceased to be Talking Beasts. But with Telmar rule various ones of the Talking Beasts, Trumpkin explains, "have gone enemy and gone dumb." Why? 

The White Witch was similar to idolatry as she was a demonic figure. Those who joined her thought they were joining the winning side. They recognized magic, a beyond physical existence and even perhaps Aslan as a power but they were mesmerized by the White Witch. Of course, any who fought against Aslan were the enemy, and they were not allowed to live if they refused to repent after Peter's victory. 

Telmar represented purely physical (not spiritual) rule. There was no Aslan and no White Witch, no spirituality even of the corrupt sort. There was simply the ethic of Sodom and Gomorrah, each man for themselves.  Talking Beasts can talk only because of the spiritual sustenance of Aslan. Joining such an ethic and worldview puts them in the same worldview as the instinctive, selfish Dumb Beasts and thus they have lost their right to remain Talking Beasts.