Are Ruthenians supposed to separate from Poland then? Or Basques from France and Spain? India, by that reasoning, should be splintered into about 25 countries. And as for Afghanistan, fuhgeddabout it. Furthermore, Louisiana and Quebec would have to separate from Canada and the US, because they speak bastardized French. How about China? It has one writing system, but several different linguistic regions.
It’s a fake argument. Hitler used it to grab Czechoslovakia the same way Putin is doing now.
I’m generally in favor of separatist movements, such as Lega Nord in Italy and the Quebec Separatists.
I would prefer that the US split up, not remain under a false unity that gives us political outcomes that combine the worst features of progressivism and laissez-faire capitalism.
If Putin takes Kiev, you may very well see a Ruthenian state in L’viv.