The presence of Neo-Nazis within a nation's borders does not give another country just cause to invade unilaterally. The idea that, because Ukraine has Neo Nazis and incorporated groups like Azov into its formal military structure, it makes the Russian invasion justified, is to implicitly accept that bigger, more powerful countries are entitled to "spheres of influence" and thus should be able to unilaterally intervene in their neighbour's politics when it suits them.
Ukrainians aren't particularly more supportive of Neo-Nazis than any other white-dominant nation in Europe – it was just an excuse by Russia to invade.
You joke (I think) but you actually illustrate why so many people are supporting Ukraine. The reaction of a lot of people to "the US should be forcibly disbanded by an international peacekeeping force" would be one of indignation and fury at the suggestion that foreign powers should violate one's home and put their loved ones in danger in order to satisfy global political objectives.