Being socialist.
The US can’t let socialist countries thrive. Or people would realize that a better system is possible. It would destroy the current narrative that “capitalism might be bad, but it’s the only possible system”.
Most things that people use to criticize countries like Cuba or NK aren’t their fault or even their choice.
When people talk about socialist countries, they don’t mention its positives like good education, affordable housing, safety, employment rates, etc.
They say things like “Cuba has old cars and slow internet” or “In North Korea most people can’t have cars and even lack vitamin C”. But all of that is because of the blockade, not because socialism causes that.
And if you dare to be socialist, the US will do everything it can to sabotage the country, no matter how many people will suffer because of that.