Another reason why this is the West's business is international law. International law is largely unwritten and based on precedent. If Putin annexes or destabilises enough of his neighbouring territories without any formal censure or international response, then such activity (e.g. Sudetenland-type "defence of ethnic minorities") much more likely in other areas and involving different nations (not just Russia). The UN would then be hamstrung by the usual suspects quoting the Ukraine precedent and blocking any action - giving the rest of the world the excuse to do nothing). The world is not made up of ethnically-based states, it is made of sovereign states. Allowing international law to change to incorporate ethnicity groupings as a basis for statehood would destabilise the foundations of western civilization.