Well if you ever figure it out let me know because I'm lost as well.
They aren't even taught the genocidal history of Communism anymore. I can't pick a point in time specifically, but I believe it became egregious with educators selectively ignoring the wholesale slaughter by the Communists in SE Asia after we withdraw from Vietnam. By failing to even mention what happened after the war, it accomplished several things at once. Notably, it gave further credence to the notion and cemented the public mindset, that the war was a giant mistake.
While the brutality of the regimes in the USSR and China were common knowledge, the extent was still fairly well hidden behind an iron curtain. This was all quietly swept under the rug to help bring the new Russia into the 21st century and no one was going to hold China and Mao's Cultural Revolution purge against them. After all what's +50MM deaths between trading partners when there's another 1B people to buy your goods or make them cheaply.
Here we are today, a bunch of useless idiots running around in Che Guevara shirts happily made in China.