Most libertarians or other freedom advocates, when pointing out the failures of nations that have attempted communism and socialism are very aware of the phrase or argument, that wasn’t real communism.
New York times for instance praising the Soviet Union system. Then when the truth is revealed about millions of deaths due to starvation, gulags, and dictatorship, well that wasn’t real communism.
Or Bernie Sanders praising Venezuela, then 4 years later when the economy collapses and people are eating garbage and their pets, well that wasn’t real socialism.
The examples are so numerous and the phrase uttered so often that it is practically a meme. In fact, in libertarian circles, it is a meme, and a point of ridicule and shame for those who repeat it.
The scam is not being perpetrated on libertarians, it is being perpetrated on the true believers. Honestly, the argument sounds pretty reasonable, and I assume that is why it works.
For instance, take the explanation provided by Professor Richard Wolff. He argues that socialism/communism is a reorganization of production where everyone has equal decision-making authority. The association people have with socialism being when the state runs the economy is wrong argues Richard Wolff. He says that socialism/communism is really a stateless, classless society. Revolutionaries such as in Russian during the Soviet Union may capture that state to induce the reorganization of production, but unless they disband the state and transition to a stateless/classless society, then it is not real socialism.
This is where a true believer says, yes, that is true, a stateless/classless society has never been established, we should capture the state, and try again. At this point, the scam has been carried out. If you missed it, it is because it was subtle. It lies within the careful description of the abolition of private property as a reorganization of production. You see the main characteristic of socialism (and of communism) is public ownership of the means of production, this is what Professor Richard Wolff means when he talks about the reorganization of production where everyone has an equal decision-making authority. This is in effect the abolition of private property. The abolition and expropriation of property requires violence, for which you need a strong state. Thus any attempts to establishing and or keeping this “reorganization” requires a state and you end up having authoritarian communism every time. Then someone says, that wasn’t real communism, and the process repeats again.
Thus the crux of the scam, of that wasn’t real communism.