Why can't I disable it? Shouldn't there be a browser extension that just rewrites all AMP links to the underlying source (if I understand right, this always exists - the page may be AMPified but it's still served from the publisher rather than from Google).

This isn't a rhetorical question, I'm interested to know whether that would work. As I see it AMP can be just as big a problem just by being there by default on Google properties as by being something you, the consumer, can't turn off.