But that's like asking about the relevance of the psychiatrist's DSM. Who's read that manual, cover to cover? Maybe only a few people, but the point of such books is to summarize the knowledge and practices that are already commonplace in the field. Likewise, regardless of how many liberal secularists have read the manifestos, the latter are useful in summarizing the implicit beliefs that are common among those folks. "Liberal secular humanism" is a real thing, a pattern owing to the fact that developed, free societies skew secular and liberal. The ideology is transferred through higher education and the middle-class ethos.

Anyway, you're not addressing the question, so maybe we can say that you don't disagree much with the latest manifesto, after all? Even if you did, you'd have to show that hardly anyone subscribes to that stated worldview. Otherwise, my article doesn't go after a red herring.