I was expecting something controversial. :)
The counterargument of course is that the region was annexed by aggression, which is dangerous to legitimize. Letting the bullies win is a recipe for creating more and bigger bullies.
But sometimes there are no good answers. I don't know any trustworthy sources of information from that area (only expats and news reporting which are all various degrees of clueless and biased).
Avoiding inflicting war on a reluctant people sounds humane. Restoring national sovereignty to a conquered people sounds noble. Impeding the spread of territorial aggression and natural resource theft sounds righteous.
Personal opinion, pragmatic I think: You can't retake Crimea without obliterating Russia. You can't obliterate Russia without horrifying consequences. Don't retake Crimea, but draw a very clear and public line, and allow no concessions regarding the next Crimea (Ukraine). This turns out to be very close to the foreign policy of most of the world.