Well the difference is one of them is a globalist side project being used as a weapon against America's enemies and just so happens to be flooded with neo-nazis and other extremist thugs that conveniently push Russia's buttons.
Saying that Russia is wrong for de-nazifying Ukraine because it's a different country is like saying America was wrong for waging war against the Taliban and Al-Qaeda because Afghanistan is a foreign country. Biggest difference being that Russia will most likely win this war whereas America/NATO lost theirs.