While I agree with your overall argument, that detail I have trouble believing.
I lived for 32 years in the United States, and not one person ever told me that they studied what socialism was in high school.
Heck, I talked to a smart young woman who was studying political science at a decent US university, Brandeis who told me, "I don't know what socialism is, but I know I don't like it."
I looked at the curriculum of her school, and indeed, there was not one class on socialism, though apparently it had been mentioned in passing in her "history of economics" classes - but there was nothing on the test.
I asked my wife, who went to a lot of different high schools all over the US, and she just laughed. "Not a word."
So I would be very curious to see this high school curriculum that even mentions Marx.
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But your underlying idea is quite right - people are easily swayed by propaganda.
In the 70s, when I was a teenager, things were a little different, and the reason is simple: we had a huge amount of spare time.
Anyone who wanted a career job, got one. Jobs were strictly 9 to 5 - maybe you'd stay late one day a week or have a few deadlines a year.
Or if you didn't want a career, or you wanted to be a musician or a writer, you could easily get a part-time job that paid the bills and allowed a comfortable if frugal existence so you to create, or just read and think.
(And this is still basically true in Europe, by the way. I have a friend who lives on about €10k a year, though he probably makes as much again in barter of services. He simply lives like a churchmouse in an officially sanctioned artist's squat - he doesn't even get government money, except for health care. He's not a kid, either, he's almost 50 and been doing it all his life.)
And there was a lot less to do. Video games cost $0.25 each. There were a handful of TV channels. No one owned a computer. Few people owned VCRs, the tapes were pricey and the quality was terrible.
People had more time to themselves - more time to think.
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There's a simple strategy to counter all of these - a proper educational system that teaches things like critical thinking.
Of course, the devil is in the details of those "things".
I did go to an American school for one year around 1970 and they had all that on the menu. In hindsight it was pretty amazing.
What happened was the Bush family. What happened was Barbara Bush's No Child Left Behind, which meant that kids had to memorize so much material that all opportunities for critical thinking were lost.
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Finally, let me be brutally frank: Americans are generally ignorant and uneducated. No Child Left Behind really did do a number on Americans.
Take, say, music. In Europe, it is impossible to go through school without getting some sort of musical education. Not so in America.
So try this test: go to a party and ask Americans to name some American composers. I asked that question of people who hadn't gone to art school for years, and I always got the same answer: Frank Zappa. With one exception, no one could name another composer.
If you think that's bad, try getting people to name a famous American painter!
https://observer.com/2018/01/how-american-students-truly-rank-in-international-testing/
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It is my belief that the issue with America is what I call idiomania - a form of infectious sociopathy which comes from people being taught that selfishness is the greatest good and that anyone different from them is non-human and inferior.
Donald Trump is the epitome of that belief.
The prevailing Republican mentality is rather like a guy who steals from cars: he causes $500 of damage to my car to get a radio that he can sell for maybe $25, yet as far as he's concerned he's ahead of the game.
Schools need to be socializing kids - teaching them compassion, teaching them that in a healthy society, individuals are willing to give things up for the greater good of society, teaching them reasoning tools not just to question accepted truth, but to actually rationally determine what is true.
But when one half of the population actively despises compassion as weakness, you will never be able to teach it in schools.
