It’s a fair question. It’s also fair to ask what they thought in 2014 as well, this has been a campaign by Moscow, a long play. But that line of thought would require an accurate and honest account of what they actually want - and it’s going to be very mixed, they’re not all pro-Russian. And this is after 8 years of control by Russian forces.
When that isn’t clear I think you have to defer to international law. You can’t sow separatist sentiment by force and then use that separatism as a pretext to invade and annex territory from a sovereign neighbor. If it genuinely was about the protection of those in the region other methods that don’t involve military invasion would seem more desirable. But it isn’t, it’s about Putin’s vision for Russia.