-- I don't think anyone here is claiming that the 20% 'rule' is wisdom or a steadfast rule.
I think the discussion here has more to do with what's appropriate for a show holder, director, or instructor/owner of a program to ask; what sort of response they'll receive; and how they can go about doing so without having someone cry discrimination (as would inevitably happen here in the states).
Because you have expressed so often that you abhor this rule of thumb, can I ask if you'd be happier with a number limit? Or do you have some other proposition as to how people should go about things?
When I rode for IHSA several years back, they had 'height/weight requirement horses' which were often ponies or light boned horses.
The requirements were that no one over 5'6" or over 130 could ride. [I don't recall if there was a weight limit for regular mounts] I can't imagine the outcry that rule would receive on this forum xD (or is it better because it's a 'hard' number? I'm not sure what the argument is here)
For what it's worth, they may have done away with this rule as I couldn't find anything about it in the 16/17 rulebook.
-- I totally agree with you.
I'm an advocate of 'live and let live.' What people do with their own horses in their own time shouldn't be anyone's business unless it's outright abuse.
Unfortunately, this conversation calls other people's discretion and reputation into play. At a show you are already paying for a judge's opinion; someone can be asked to dismount for abusive behavior or inappropriate tack--I don't see whys judge wouldn't have discretion over this, too.
The flip side (which, I also totally agree with you) is that, as an exhibitor, you always have the right to pack up your things and go, and choose not to associate yourself with or deal with that judge again.