The unclear explanation also disturbing considering that the abuse of logical fallacies has almost become an internet meme. The No True Scotsman fallacy seems particularly popular in this regard.
I've noticed a common trend in arguments of the following sort:
A: No Communist dictatorship has ever had long term economic prosperity.
B: What about the United States? It's had incredible economic growth for over a hundred years.
A: The United Sates isn't an communist dictatorship.
B: That's the No True Scotsman fallacy.
You have to be doubly careful with communism - McCarthyism and the "Red Scare" were clearly a little much, but the trendy counter-reaction tends to be at odds with history. The US government was infiltrated by actual communist spies (to the extent that they practically ran the State Department in the '50s), and it's hard to argue with the hundred million or so it killed in the 20th century. It's easy to say that there have been no properly realised communist societies/states, but an honest account has to hold the idea responsible for the ubiquitous oppression and murder committed by regimes attempting to create them.
I won't argue that the Americans you talked to can give a reasoned condemnation of communism, but with its historical baggage the burden tends to swing the other way. It's hard to have a rational argument with a lot of people about Nazism, but it's hard to criticise people for trusting that it's not for them.
I've noticed a common trend in arguments of the following sort:
A: No Communist dictatorship has ever had long term economic prosperity. B: What about the United States? It's had incredible economic growth for over a hundred years. A: The United Sates isn't an communist dictatorship. B: That's the No True Scotsman fallacy.