Every liberal does it too, from center right radlibs to far-right "conservatives": the most extreme right fringe liberals hate the mainstream liberals for not being bigoted enough, the mainstream libs hate the radlibs for not being cruel enough, and the radlibs hate the left for not being chauvinist enough.
Denouncing chauvinism in particular is like a liberal moral event horizon, a cardinal sin against their self-interested belief in the righteousness of the imperial hegemon that keeps the treats flowing at gunpoint.
I just love the image of some liberal consciously thinking "I hate anyone with better politics than me," like the idea that they'd label their own politics as worse than leftism
I think the contempt just manifests as cognitive dissonance.
In the manner MLK wrote in his Birmingham letter, paraphrasing: I agree with your aims but not in the manner you seek change through.
Their politics are informed from a position of privilege, strength, idealism, and at best, sympathy. Not solidarity. So sympathy-but-not-solidarity compromises the efficacy and urgency of political demands and action. An expectation that a large protest is the equivalent of forcing the state to capitulate or concede to popular demand; protests are expected and in action treated as a regulated parade/rally that neither threatens property nor order. It is supposed to be "virtue signalling".
Anything that transcends cosmetic protest is treated as civil insurrection.