2nd Largest Insurrection in U.S. History... that few have even heard of.
Interesting list. Props (and rep) to Bearded_Menace for starting an intelligent thread.
I know any list is going to be subjective. But in my mind, the most shameful events are those where violent acts are allowed or encouraged by a government against weak or defenseless individuals or groups. So one that I would put on that list is the events that led up to the Battle of Blair Mountain. I doubt many (any?) people here are aware of it, since it happened in an area of the country that gets little attention outside of being the butt of jokes (West Virginia). You may not know about the Battle of Blair Mountain and you may not care about West Virginia. But you've probably heard the name Mother Jones (yeah, she was a real person) and know the name Hatfield, from the Hatfield and McCoy feud. Mother Jones and Sid Hatfield are part of the story.
I think it's important to see what happens (and happened) when capitalism goes unfettered. In the early part of the 20th century, the big coal mines tried to keep the people of southern West Virginia as indentured servants, working in their dangerous mines, being paid in company script and living in company houses. Anyone who even though about joining the union had their belongings thrown out in the street by deputized Baldwin-Felts goons. They'd usually do it when the men were at work or away, and they'd focus on the women and children. After the sheriff of Matewan, Sid Hatfield (see the movie "Matewan"), was murdered by some Baldwin-Felts agents, the miners bucked on the mines and started a heavy United Mine Workers drive. A battle ensued at a place called Blair Mountain. About 15,000 miners took up arms. Mother Jones cautioned them not to take up arms, since she feared there'd be a heavy bloodshed. Other than the Civil War, this was the second largest insurrection in U.S. history. The governor of West Virginia and the President of the United States (Warren G. Harding) sent in troops and airplanes to support the coal companies' interests. General Billy Mitchell even commanded a unit of bombers which dropped surplus WWI bombs on the miners. That was a lesson to the working/poor people of the time: know your place or you'll be killed by the government.
Short term, the coal companies won. Long term, the United Mine Workers won. I'm not a union man, simply because I believe their mission has gone off track since the 1970's. But I do realize there was a sad time in this nation's (recent) history when the working man was considered nothing more than an expendable tool to monied interests... and the U.S. government had no problem with that. Just like Wounded Knee, the Trail of Tears, slavery or women's suffrage, I think what happened at Blair Mountain should be on this list. We either stand for the "American ideals" that we claim to stand for... or we don't.