"Wherever there is a definite territory, and we can make a plebiscite on this territory, and ask the people who live there, if the want to be an independent nation or not, then, if the answer is yes, they should have an independent state, no matter what. That's what I think.
Chechens want it? Let them have it. Taiwan wants it? Let them have it."
Sounds nice, but utopian. What if some ethnic groups consider their borders unjust and want piece of their neighbors ? I.e. once Chechnya and Dagestan were united under Imam Shamil in 19th century during a war against Russian Empire. Chechnya in its present borders was drawn by Stalin and then redrawn by Kruschev. What if some Chechen Nationalists will demand return to Chechnya "historic borders". What if Islamists in Chechnya will say that Chechnya is only the first step of the "Jihad" against Russia and will call for "liberation" (read Islamic revolution) of the entire North Caucasus and beyond ?
What about American Southwest that is increasingly Hispanic ? Some Mexicans and their supporters who are illegally entering US through US-Mexico border are claiming that they are settling on the "historic Mexican homeland" that was "stolen" during Mexican-American war of 1848-1849.
What happens if Germans will demand return to previously German lands in Western Poland from which they or their ancestors were expelled at the end or after World War II ?
What if they want to secede from Poland and reunite with Germany ?
Who will determine which claims to which land are more valid ? On what basis ?
You see what happens when respect to currently internationally recognized borders (no matter how they came to be previously) is completely substituted by emotions about history and sympathies to this or that ethnic or national group? We may open Pandorra box of historical claims and counterclaims.