Let me flip that a bit, please. It's indisputable that the Articles of Confederation aimed at a "perpetual" government, and the articles could only be altered via the ratification process with 9 colonies or states agreeing. It's also indisputable that the purpose of the Constitution was to further allow a stronger federal govt, in the areas of power that the federal govt would be supreme, while the BoR forbid the federal govts (but not the states) from passing laws effecting personal rights.If those claiming secession is permitted because it doesn't say it's not by the Constitution, how can they claim the Union is no longer Perpetual when it was, clearly, in the beginning and the Constitution does not say it no longer is?
So, from those undisputed facts, where does one find a power for one or more states to secede without using the Constitutional provision for amendment?