Russia is as morally entitled to invade Ukraine as the US was to invade Afghanistan. It's really that simple. You can say moan about Saddam being bad but where from where does the US derive the moral authority to impose its will onto sovereign nations?

Your framework allows for invasions over fake WMDs and fake Nazis alike. Russia didn't sanction the US over Iraq, in the spirit of peace and cooperation between nuclear states the US could afford them the same courtesy.

If you can justify Iraq you can justify Ukraine. Personally I don't agree with invasions anywhere for any reason not do I believe in the concept of "world police". That's just forcing one people's will upon another and denying them the right to destroy their own tyrants and seize their own destiny.