-Many people appear to think either that (P) all social constructions are bad, or (P*) that belief in (P) is central to SJWism. Hence much mockery has aimed not to point to clearly beneficial social constructs (e.g. respect, love, money) but to suggest that almost anything can be a social construct (e.g. the penis).
A more sophisticated view is that something's being a social construct points not to it being bad, but to it being replaceable or at least malleable. But even this is perhaps too simplistic. Musical harmony is a social construct - while in the West we use a 12-tone scale, many other cultures (or composers within the West, e.g. Harry Partch) use different scales with greater or smaller intervals between notes - it is hard to see how we could overturn many aspects of harmony. (Though we could of course tweak it in particular ways, e.g. moving from equal temperament to just intonation).
(edited to add: this is probably old hat to anyone who reads my blog. I'm not trying to say anything especially original here, but it occurs to me that it would be useful to have something to point to, making this point, which isn't the length of a Slate Star Codex post or three)
-In a liberal society, we want both a principle of exclusion and a principle of inclusion. Thus our society can take in and integrate outsiders, but need not roll over in the face of those who threaten it. A "Propositional Nation" goes much of the way towards this - anyone who affirms the key propositions can become a citizen, people who do not affirm those principles cannot. Contrast this with historical or blood-and-soil nationhood, as exists e.g. in UK and Scandinavia. (France is a weird case - it ought to be a kind of propositional nation given the way French nationhood developed after the revolution, but it's still more of a blood-and-soil nation). Blood-and-soil has practical advantages - among other things, a country can hardly expel native-born citizens for their political views - but lacks such an easy criterion of inclusion. Should places like the UK aim to become more "propositional" in terms of their national spirit? Can they do so without abandoning their present identities? (Can "loyalty to the queen" function as the kind of proposition that would bind a nation?)