There's liberalism as a political theory (with all its variations, from classical to Rawlsian), which is admirable and distinct from Maoism. But there's also the "liberalism" that's more accurately described as "the set of cultural, social, and political beliefs broadly held by the college educated, urban, professional class." And professing adherence to Maoism is entirely acceptable in that milieu, in a way that professing adherence to e.g. the Religious Right or Trumpism is not. (The fact that this judge's commitment to Maoism is purely symbolic verbal signaling and not linked to any actual activism is besides the point.)

Imagine a judge said he was a committed fascist who would judge students on that basis, regardless of the quality of their arguments. Would that be considered acceptable in the same way the Maoist judge is? Just last night I had dinner with a friend who was telling me about a family member's encounter with Maoist justice: he was murdered by being thrown down a well during the Cultural Revolution.

Or, take the other angle. Suppose you had a staffer on Fox News who spent his off hours writing racist screeds on white supremacist forums (this has actually happened IIRC). Would you take it as a single extreme example that's not worth thinking about, or would you take it as indicative of some deeply troubling aspects of the modern Right?