...But this dodges the blow by confounding the claim to secede at will, with the right of seceding from intolerable oppression...
Madison is saying that it's okay if you are facing intolerable oppression. So who gets to decide if their oppression is intolerable?
Obviously King George did not think the Colonies were intolerably oppressed. For that matter, neither did the third of the population that constituted the British loyalists. Neither did the populations of Canada.
It would appear that if we follow the example of the founders, it is they who decided the oppression was intolerable, while obviously the King disagreed.
So who gets to decide? The people who want out, or the people who want to keep them in?
It's pretty obvious King George didn't give a damn what the Colonies thought. That's the way tyrants operate.