> I would not be starkly opposed to Crimean independence, nor even Russian-integration, but in essence it looks like Russia took Crimea and then held a fake referendum to legitimize it.
> But the question always goes - where do we draw lines. Should we support the concept of the Confederate States of America seceding from the United States? If California or Texas wanted to secede, should we support it? Wales? Okinawa? Quebec?
Why drawing a line? It's either you allow everyone to choose their country, or noone. Allowing Crimea but not California, or allowing Kosovo but not Mexico and allowing Slovakia and not Catalonia is the worst solution. Right now, it's completely arbitrary, and this arbitration is what leads to wars and conflicts.
I would say, let them all decide for themselves.
Do you want to allow Ukraine to be independent? Then also allow Donbas republic to be independent of Ukraine, and consequently allow cities in Donbas that wish to stay in Ukraine to secede from Donbas. And even within those cities, allow neighbourhoods that want to stay in Donbas to stay.
Why not, if that's what people want? And that would mean no war. Yes, it may be complex in an administrative way. Who wants to show passport to cross the street and go to the store. Or to cross borders twice when going to work? Or to apply for a work permit? But exactly that complexity would quickly lead to different agreements and territorial rearrangements if people decide it's better for them. Again, why not? If they agree, they can change the state every year or so. If you let people power to decide, they will be more responsible for purely selfish reasons. That's how capitalism works, why not politics?
As soon as you draw a line who can and who can't decide, you are creating a conflict that may or may not lead to war and other atrocities.