RE: I am saying that we should “let” Ukraine work out its own issues with its neighbor
So, no worldwide sanctions in coordination with our allies in Europe for what Russia did, just act as if everything was as normal as it was before?
And if Russia did the same to Moldova, Estonia, Latvia and the rest, we “let” these countries work out their issue with their bigger neighbor as well, and we simply act as if this is not our business?
Precisely. And how do we define "normal as it was before" -- Kiev allied with Russia or the new regime that we helped to overthrow the earlier government? And why did we do that?
America rightly prohibits foreign powers from meddling on our borders (even our hemisphere, per the 1823 Monroe Doctrine), and we would be wise to leave other powers' borders alone, too. Borderlands provide healthy buffers between competing powers that help to prevent wars from starting inadvertently; Forging competing military alliances along another power's border can only be interpreted as an existential threat.