It has often puzzled me why people want to "belong" to an organisation, whether as a member or as a guest participating in that organisation's events, and then complain about the rules
Exactly the kind of progressive, dynamic, forward-looking thinking that AUK is renowned for.
I don't see any problem with discussion (not complaining) about the rules to assess general opinion and stimulate debate prior to, as you say, putting forward a motion at the AGM. That's one of the things forums are for.
"Like it or lump it" is a bit last century for my tastes.
what would your proposal be ?
That when someone on a public discussion board suggests something that is unusual or not yet tried, it gets the courtesy of a discussion (and yes, I know we've done time limits to death and I'm one of the people who doesn't want to see that changed) rather than just being told, effectively, to sod off. Intentionally or not, Martin's post was basically telling another rider whether they may or may not ride audax.
An individual rider might decide they don't like the rules, realise the weight of opinion is against changing them, and choose not to do any riding that fetters them in that way. But it's up to them, not self-appointed AUK hierarchy.