Usually that would be the case. However, the Ukraine is different in that the areas concerned are along badly drawn borders and that the people wanting independence are Russian people - many of them holding Russian passports. Ideally, both sides would go for a referendum - but this is the reality of geopolitics in that part of the world we're talking about here.
It's either that Ukraine accept the new regime in Kiev and remains unified, or the East of Ukraine somehow detatches itself from Ukraine with the help of Russia. As I support self-determination, if the west won't grant that self-determination option then Russia won't be doing a bad thing by providing it.

