This puzzle came really close to being brilliant, but was let down by a few technical flaws, which is a shame. The quotation is not vital to solve it (though the D-word is a useful hint), but the six circled letters were, since without those the unclued words are utterly mysterious. So to put the circled squares so heavily dependent on the very unclued words that you can’t guess until you have them was, I think, unkind.
A question for those with Brewer’s to hand: there’s been discussion of the problems with 23a (which seems to have been docked its terminal ‘L’) and 10d (inexplicably pluralised) — does the relevant, if hard-to-find, entry in Brewer’s confirm those variants (no L, plural)? Or do they appear to be a setter’s slip?
For me, this puzzle admirably embodied the last three words of the quotation!