we are as a whole responsible for making the world a better place. everyone with their capacity and their ability to do something. now, i am not trying to judge what you are doing, nor am i suggesting you are not doing enough already. that's not the point. by living in the US you are however in a better position to work on this particular cause than i am living elsewhere. not because you are responsible in the sense of being guilty, but you, and everyone else in the US, is responsible in the sense of there being a wrong that needs to be righted.

otherwise we could just say nobody is responsible because it was all someone else. but if that someone else is not alive anymore then it is up to the current society to step up and fill in. guilt is not required. would you help orphan children whose parents died in an accident even if you were not involved? then why not help these people who have been deprived of their land and are now without the ability to govern themselves? the people of israel got their ancient homeland back after 2 millennia and were allowed to form a sovereign nation long after anyone could reasonably be called responsible for taking their land away. so why not do the same of the native american nations too?

the question is not: are you responsible? but: is there a wrong that needs to be fixed, and are you in a position to contribute to fixing it?

but to your last point: this has nothing to do with being upset about supersonic jets. actually i believe as far as it is reasonable native americans would be upset about noise pollution too, so you would probably be arguing their side here anyways.