Not defending them or even Luigi but I would argue a lot of it is the abysmal labour institutions the USA got (lots of union busting, few modern laws against modern exploitation and classical institutions are undermined politically and legally).

And the growing class divide in the USA I think is the reason why folks are increasingly seeing violence against the upper class is seen as the only option.

Again doesn't mean it makes it right, but it explains why it is almost only an US phenomenon.