So if the Chinese going into a place with an oppressive system, and making it 'better' is ok, then I guess it's ok for the Americans to do it too.
But the Americans have turned dozens of countries to shit. Iraq used to be a pretty stable place and a model for progressive secular islam. Now it's one of the world's most dangerous countries and a breeding ground for fundamentalism.
China in Tibet, well it's much more nuanced. The Chinese haven't wreaked havoc there like the yanks did, then again it's very heavily policed.