the euphemism treadmill is a description of linguistic patterns, not a get out of rule free card
Using ableist language as insults is always bad, even if the words seem innocuous. Some may reference the "euphemism treadmill" to try to justify their behavior, but it's crucial to understand that the treadmill is merely a linguistic observation. It does not exist to normalize ableist behavior.
today i learned that 'cretin' has ableist origins. just hearing the word, and being completely unaware of its origins, i assumed it had racist origins and was somehow related to the isle of crete.