The risk in over-enthusiastically endorsing the self-determination argument is that it can be equally applied to support shearing off the eastern regions of the Baltic states, some of which have ethnic Russian populations in excess of 50%, in which the Russians have been stirring up discontent for some time and some of whose population wouldn’t mind being reunited with the Родина.
Self-determination was one of the arguments for ceding the Sudetenland to Hitler, after all. Besides, any idea that traces its origins through Woodrow Wilson is likely to be pernicious.
That said, I believe that most nations, especially continental-scale railroad-era empires, would be better off and their residents happier were they to split up into ethnically and culturally homogeneous smaller polities. Every study I’ve seen shows an inverse correlation between the size of countries and the self-reported happiness of their citizens. Then, apply the principle recursively. You end up with secession to the level of the individual and replacement of coercive authority with voluntary association.
Lysander the Great saw this coming a long time ago (1870) in “No Treason”.