As far as Wounded Knee goes it is my opinion that the whole damn US Army was spoiling for a fight. They had had enough after 50 years of Indian Wars.
Massacres over the years were mostly caused by turf wars or religious wars. My home, the State of Nevada has the slogan "Battle Born" I am proud of that. This country was built be white men with guns. Just a fact no opinion.
If there were no guns then it would have been done with spears and knives - plain and simple. Roman style, manifest destiny is a powerful thing.
I guess my point is large masses of PO'd folks with auto weapons would make for a mess at best - the USA IS NOT Switzerland or Sweden etc.
Different cultures, different people entirely.
Some of whom were using them to force other people to build it for them.