Lenin was a political opportunist and Stalin most likely faked Lenin's will to appoint himself after his death. The Bolsheviks also murdered/incarcerated plenty of leftists and disempowered the pre-existing worker coops and trade unions through centralization.
Anarchists, syndicalists and other leftists were literally building decentralized structures before the Bolsheviks swooped in and decided the public would need decades of ideological education before it could be trusted to make any decisions about their lives and "helpfully" started making the decisions for them. It doesn't help that many of the leftists outside Russia who were critical of Bolshevism were murdered by German paramilitaries and later more indirectly by the USSR while trying to fight fascism in Spain.
Saying you have a good understanding what "left" is because you were born in the USSR is like saying you have a good understanding of what pasta is because you've been eating Yum Yum noodles for a decade.
Have you read Kropotkin? Bakunin? Proudhon? Bookchin? There is a wide range of leftist thought outside the very narrow niche within Marxist-Leninist-Maoism that still uncritically defends the USSR.
You try to explain the consequences of communism with "few bad apples"; well, at least it's not a "no true scottsman", I have to give credit for that. However, there have been so many cases of leftists coming to power and building a state, and the only one I know that didn't end is tragedy was Israel — and even it resulted in financial crisis and eventual move to capitalism.
Of course, it's opportunists and sociopaths who come to power. You're absolutely right about that. But it would be silly to explain all these outcomes as fault of particular individuals, even if they are at fault. It's the principles behind the system itself, which make it vulnerable to this kind of attack.
Essentially, the problem is with this: every kind of leftism makes moral behaviour nor a matter of personal choice and responsibility, but something mandated by the state or a quasi-state organisation. This sounds very good in theory, especially for the people who are sensitive to the wrongs of the world. But in practice, it makes those organisations infallible and creates in their place a perfect vessel for said opportunists and sociopaths.
State power is like The Ring from LOTR. It's very seductive to use it for good, but absolute power corrupts absolutely. It should be not used, but destroyed.
You do know that anarchist ideology is literally defined by the opposition to states and state-lile structures, right?
It seems odd to tar specifically anti-statists with wanting to create a state. Anarchy being literally the antonym of hierarchy, statism is the complete antithesis of anti-authoritarian left-wing politics.
You're thinking of Stalinist/Leninist authoritarian communism, which certainly doesn't encompass all of left-wing ideology, only a niche.
When Stalin came to power, one of the first things he did was too purge all the anarchists and other non-authoritarian socialists. Thus most leftists despise Stalin and what he did. Mao, too.
Yeah, I think that was the intended reading of that reply given the obviously similar phrasing.
However there's a word for anti-authoritarian leftists. We're called anarchists. Not all leftists are anarchists and not all leftists are anti-authoritarian. Even authoritarian leftists (or "statists") generally believe in the end goal being the ideal of a stateless, classless society.
Statists just tend to believe the only way to get there is with an intermediary socialist state established through a communist revolution and led by a vanguard party who directs the economic, social and philosophical evolution of the people towards bringing about communism. The differences between those groups are largely about what that intermediary state should look like and at what point it can be dissolved.
Some of the aspirationally communist states of the 20th century justified their continued existence with communism having to be rolled out globally simultaneously for it to b successful. Some instead argued that what they had achieved was "real socialism", heavily implying that's as good as it gets and any critics were utopian idealists who'd rather tear down the local optimum in the hope of an unachievable ideal. The USSR opened its markets and collapsed under the dual load of its bureaucrat aristocracy and capitalist oligarchs, China pivoted to Dengism to contain their "capitalist experiments" with the promise of a greater good coming from the temporary toleration of exploitation.
But for anarchists (and mutualists, who fall somewhere between anarchism and statism) the biggest problem tends to be that they usually either start out or end up surrounded by nation states with standing armies who want none of their nonsense.
The most promising approach seems to be dual power, i.e. building anarchist structures[0] within existing states through cooperation and solidarity so that when they inevitably collapse in the future, the people can fall back on those structures as an alternative to just reasserting the old (hierarchical) power structures.
[0]: To preempt the obvious joke: contrary to the portrayal of "anarchy" in most media today, anarchists don't believe in no organizations, just no hierarchical power structures, i.e. usually they agree with consent-driven forms of bottom-up organizing. The one exception tend to be egoists (see Stirner), but most anarchists try to ignore them because they're weird.