I agree that radicalism can be hypocritical and counterproductive. I'm not sure how that engages with the main point of this article, though.
Humanism and progressivism are gambles. I'm not a card-carrying humanist, liberal or progressive. I criticize both sides of the political spectrum. My point here is just that we should be aware of what's really at stake instead of being content with cliches and conventions that hide the political truth.
Indeed, progressives need some social stability since no one wants to live under a reign of chaos. But conservatism isn't just about stability; it's about the most stable form of society, which is obviously the "natural" one, i.e. animality (dominance hierarchy, pyramidal social inequality, etc).
But I take your point that purity in either case is futile. Just as viable conservativism is stuck with conserving some results of progress, progressives are stuck with building on a conserved social foundation.