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.
"You're not normal! You CAN'T be normal, because then I'll no longer be THE normal! SHUT UP, THIS IS THE CONDITIONER FOR THE THREAD BY WHICH MY SANITY IS HANGING!"