Ordinary language is all right.
One could divide humanity into two classes:
those who master a metaphor, and those who hold by a formula.
Those with a bent for both are too few, they do not comprise a class.
'I can't speak for…' a person, someone else, but likely someone I know, even someone I may know quite well.
But 'I don't speak for…' an institution, a profession, a party, a group, unless they've said so; nominated, elected, chosen me.
(Yet it is more likely 'I can't speak for all…' than 'I don't speak for all…'. The former evinces awareness of a representative potential in what one will say. The latter denies a presumed representative power, in some cases to claim a more partial but still representative one.)
Speaking up; speaking out; speaking out of turn.
Speaking for oneself; speaking for myself; speak for yourself; I think I speak for all of us when I say; he speaks for all of us.
Voice; calling out; calling out to you; calling you out; calling on you; calling upon you all.
Voice; having a voice; having a say.
Finding your voice; having your say.
Pirate Prentice's 'Firm', i.e. the Special Operations Executive (a successor to Section D of the Secret Intelligence Service, aka MI6), is the earliest They in Gravity's Rainbow.
Late in the book, when he finds he still works for the Firm, as a 'double agent'—for '… no one has ever left the Firm alive, no one in history—and no one ever will'—Pirate begins to cry:
'… he understands where he is, now. It will be possible, after all, to die in obscurity, without having helped a soul: without love, despised, never trusted, never vindicated—to stay down among the Preterite, his poor honor lost, impossible to locate or to redeem.'
OK, Herder, this sentence has eight exclamation points in it. And not all at the end!
Herder uses so many exclamation points!
The Dude's only form of ID is a value club card from Ralph's. But even it says 'Jeffrey Lebowski' on it.
The joke about lacking proper identification is to only have a library card. Only having a gym ID doesn't strike the same note, even if it too lacks a photo. A library card is an emblem for books, words, for just the things not to be trusted by anyone who asks to see your ID. (Only certain books, certain records, count for them.)
Libraries are themselves trusting places.