Not well read on Chinese history are you?

It might be better put as "the Han Chinese think everyone else is a barbarian savage, but also, they prefer to leave their vassal states to run their internal affairs themselves. They don't call them barbarian savages on a daily basis."

I see this pattern a lot in the US. I don’t fully understand where it comes from, the early puritanical religious roots of the colonial period?

large scale "boots on the ground" invasions are pretty hard to sell to the american public. they don't generally want to see american soldiers die without a good reason. retaliating against the people who harbored bin laden is already a pretty good reason, and liberating the subjects of an oppressive regime is icing on the cake. of course, it's hard to paint a regime as oppressive without also calling them "backwards". after all, if they were as advanced as us westerners, surely they would have a free democratic society already. /s