The most effective advertisement for communism[1] is capitalism.

[1] Not the failed Soviet Union experiment, but the idea of broadly shared equity and many aspects of life being done for their intrinsic value rather than money.

Oh yeah, the reality of communism was so great that communists (all over the entire planet) built walls to prevent people from leaving.

That way they made sure you enjoy it to the fullest.

The most effective advertisement for capitalism should be that you can be communist under it, meanwhile under most communist countries you'd get the firing squad for speaking against the regime

Authoritarianism will reliably produce such outcomes regardless of the economic system or ideology at play, and violent revolution/vanguardism will reliably produce authoritarianism.

Vanguardism and violent revolution are a failure, that doesn't make capitalism the only alternative. Indeed, that's entirely orthogonal.

Plenty of capitalist states have committed similar atrocities. An obvious example being the early United States - the transatlantic slave trade and the various death marches inflicted on Native Americans are every bit as horrifying as the crimes of the USSR, and were committed explicitly to obtain labor and real estate (notice these are both forms of capital) for our burgeoning capitalist economic system. Yet the people who claim the USSR proves communism is necessarily violent don't seem to take this as evidence that democracy or capitalism are similarly irredeemable.

If you aren’t able to distinguish communism and revolutionary authoritarianism you have very little right to enter these sorts of arguments with any sort of authority. Take your US propaganda view of political and economic systems and run off elsewhere.

You are describing totalitarian authoritarianism, not communism.

This is why I felt that the distinction between communism and the failed USSR experiment was necessary. Sadly, whenever many people from the US hear the word communism, they immediately assume it means the Soviet Union. Communism was one of many aspects of USSR, many of which were much less desirable by its people.

Could you provide one example of communism that did not end up an authoritarian regime?

Communism is just not compatible with freedom. When free to choose, societies do not become communist, they embrace production and trade. You cannot achieve what communists want without extensive use of force

It has not been implemented on a state level without the state also being totalitarian. There have been few tries to do it on a state level, anyways.

However, on a town or district level:

1. Primitive Communism — basically all human history before the agricultural revolution.

2. The Paris Commune — Paris was run by its workers for a few months before bloody suppression by capitalists.

3. The Israeli Kibbutz movement.

4. The Zapatistas in Mexico.

5. The Rojava region in Syria.

Overall, there are many cases in which communism has been successful and sustainable for a long time at a district scale. In case of primitive communism, for thousands of years.