It's one of the greatest legacies of the US unions. E.g. May Day as the international day for workers demonstrations came about largely in recognition of the sacrifices of the Haymarket Massacre, and thanks to the AFL reiterating it's commitment to the 8 hour day by planning new demonstrations for May 1st 1890.
Less than 100 years ago, this stuff happened. Far out. I truly can't comprehend the strikebreakers getting away with... Well, cold blooded murder. Massacres. It's horrible.
Very simple: the striking workers were considered criminals - rabble that no upstanding citizen would want to get associated with. Today, they'd be called terrorists.
Now think about how today, the American military gets away with bombing weddings...
Do you have a citation for who said your quote - I'm not an American but that really doesn't sound like something one of their founders would have said (of course, I could well be wrong!).
"Without a blatant display of humor, it is impossible to create a parody of extremism or fundamentalism that someone won't mistake for the real thing."
The truth is that thousands of workers died in a world wide struggle for humane working conditions during the 19th century.
In Chicago: https://en.wikipedia.org/wiki/Haymarket_affair
In 1921 bombs were dropped on striking coal miners in West Virginia: https://en.wikipedia.org/wiki/Battle_of_Blair_Mountain