I don't think "no true Scotchman" means what you think it means...
It's about criticizing something as invalid, BS, problematic etc. -- is not even about saying something X doesn't belong to an idealized category.
It's about shifting the discussion to "X doesn't belong to an idealized category" AFTER you were OK talking generally about it previously.
This means that when one talks morally/ideologically/etc. about what constitutes "a true scotchman" (e.g. not in the plain sense of citizen of Scotchman") it's not a fallacy to ascribe certain attributes to the notion (because "true" here essentially means "ideal", "most representative" etc, instead of merely "actually existing").