Thanks. You reminded me of another funny thing about communists and Libertarians. They say the same thing!
A communist always insists that REAL communism has never had a chance to be tried. I am sure you have debated a communist or two in your life. Pretty soon, they are passing over the REALITIES of communism, of what REALLY happens, and are tellign you Stalin wasn't really communist, he was Stalinist. Pol Pot wasn't communist... and on and on.
Libertarians do the same thing. When people talk about flaws in the free market (flaws that usually are the result of corrupt humans), Libertarians are left saying, "but this isn't a free market, that wasn't a free market, there never really has been a free market!"
I think you're misunderstanding real reason why communist ideology fails, and because of that, you're missing an important distinction between the way communists and libertarians think. Communists believe a completely impossible thing: They believe that they can reliably change human nature to turn us all into mindless automatons. They think that with the right authoritarian indoctrination program, the vast majority of people can be made to reject all natural impulses towards self-preservation and act completely selflessly with only the good of the collective in mind.
As a consequence, communists believe they can design an economic and political system with complete disregard for actual human nature. Most importantly, they completely ignore the concept of moral hazard.
To give a small example of what happens when you design a system without regard for moral hazard: Already assuming their indoctrination program will work, communists blithely handwave away every warning about the obvious incentives for individual workers to be lazy and unproductive under communism (since they do not individually benefit from their own productivity or individually suffer for their own sloth). This natural and completely predictable problem of moral hazard drastically reduces the economic output of a communist workforce in practice.
To give a bigger example, communists think they can centralize all political and economic power without the evil ever seeking those positions of power. After all, collective ownership is completely impossible in a group of more than a few thousand (let alone a whole nation) without empowering a bureaucracy to manage it all and dictate how resources will be used. The larger the communist society is, the more distant this bureaucracy becomes and the more it resembles an oligarchy. There is no avoiding this, but communists paper it over with platitudes about everyone working solely for the benefit of the collective (due to their foolproof indoctrination program

). The communist power structure is completely unable to handle ordinary human beings with ordinary human motives. Moreoever, once you introduce malignant narcissists and psychopaths (or even idiots) to the system, everything predictably falls apart, even on paper. Not only do psychopaths exist, but they don't just "happen" to land in positions of power over others. Rather, they're particularly attracted to positions of power, and they actively seek them in a way nobody else does...and since political power is necessarily totalitarian in a communist society, communism enables psychopaths to their fullest potential for evil. Barring complete revolution, there is no limit to the amount of violence and coercion a totalitarian government can commit.
Communists cry foul and say "true communism" has never been tried, but they're WRONG. When they say this, they really mean "communism with an ideal population of completely mindless drones has never been tried," but in the sense of the concrete power structure of the system, it HAS been tried, over and over and over, and it's failed every time for the same reasons. When you create a state with absolute authority over every person's life, it's an unbelievably stupid pipe dream to think that competent, or even benevolent, people can be perpetually counted on to maintain positions of power in that system and behave responsibly.* Beyond the problem of evil, communism becomes more and more economically unfeasible the larger it gets in scale. It's economically insane to think a cadre of supposed intellectuals can correctly guess at the needs and wants of a large-scale economy and work out the logistics. In contrast, the supply and demand-based price mechanism in the free market provides strong signals about exactly what goods/services are demanded (i.e. needed) and where (and how much/many), in the form of tangible incentives for meeting these needs and wants.
On the other hand, when libertarians say that a free market hasn't been tried, they're actually RIGHT. Unlike the communist power structure - i.e. the actual underlying system - the libertarian power structure has never been implemented. Pretty much every time anything goes "wrong" in the free market, it can be traced directly back to the market's natural - and predictable - reaction to some coercive (non-libertarian) government policy. In general, the closer we get to libertarianism, the better things get. There are exceptions of course, such as when we move towards libertarianism in certain policy areas in the wrong order. For instance:
- Deregulating is a libertarian policy...but it would be disastrous to remove regulations on telecom monopolies before getting rid of their government-granted monopoly contracts and allowing time for competition to start up. However, this would be a failure of government-granted monopoly contracts (which the regulations merely "patched up")...NOT a failure of the free market, since those monopoly contracts obviously do not belong in a free market.
- Deregulating is a libertarian policy...but it would be disastrous to remove reserve requirements on fractional reserve banks while legal tender laws, capital gains and sales taxes on precious metals, the Federal Reserve, the FDIC, federally mandated and protected fractional reserve banking, Fannie Mae, Freddie Mac, regulations forcing banks to extend credit to bad bets, etc. still exist. However, this would be a failure of one particular libertarian policy mixing poorly with a slew of other coercive policies...NOT a failure of the libertarian policy itself.
Now, is it possible to maintain anarcho-capitalism without the power structure being corrupted and a single monolithic state emerging? Is it possible to maintain a minarchy without the power structure being continually extended in size and scope until it approaches totalitarianism?
Those are important questions, but those questions drive us to build better checks and balances into our power structures and institutions (centralized or not, though decentralization is a check/balance in itself). Whereas communists say that communist power structure would work if only the PEOPLE were different, most libertarians are much more intelligent from a systems design standpoint. Like all other totalitarian power structures, the communist power structure gives psychopaths (or mere idiots, at BEST) complete control over everyone's lives from the get-go. The closer you get to libertarianism and decentralization of power, the harder it is for any central authority to achieve that control.
That is the point. Probably the single most important lesson we can learn from human history is that centralized power - especially centralized coercive power - enables evil and leads to misery and suffering...especially as it becomes more and more centralized. No matter how much of a challenge it would be to maintain a libertarian society and keep a centralized authority from usurping all power for itself, these challenges still pale in comparison to the sheer masochism of trying to keep already-more-centralized systems under control, especially those which already have the complete infrastructure for tyranny from their inception (i.e. fascism, socialism, communism).
Perfect libertarianism may be nothing more than an ideal - an approachable but never reachable asymptote - but libertarians are not wide-eyed utopians. The fatal mistake everyone else makes is refusing the recognize or understand the immense and prohibitive dangers of ceding control over their lives to a centralized power. The derogatory connotations of the word "utopians" belong to people who naively think centralized totalitarian power may turn out okay, "as long as we put it in the right hands."

Libertarians recognize the folly and built-in danger of such power structures and advocate moving as far away from them as possible. If we can get enough people to fully understand the dangers of centralized power and the nature and prevalence of narcissism and psychopathy (and pass on that knowledge to their children, etc.), we MIGHT have a chance at perpetually containing the problem of evil...but without getting people to understand these things, you're pretty much right that we have no hope of ending the cycle of freedom and tyranny. Personally, I'd like to think it's possible to make this stuff "common knowledge," like 2+2=4 and such...human civilization is still pretty young after all, and it's not like history's been repeating for hundreds of millions of years or something (to the best of our knowledge

).
There are other institutions which can obtain power over people's lives, as you've mentioned, like religions and corporations (which wouldn't have personhood or limited shareholder liability anyway if not for state mandate, remember). However, nobody recognizes these institutions as legitimately possessing the powers of violence and coercion. Because of that, when evil or incompetent people take over these institutions, the "entry barriers" for competing against them and offering alternatives - in both the market sense and the mindshare sense - are orders of magnitude lower than competing against an out-of-control state...and the more coercive powers you grant to the state, the more they will be abused and the quicker it will spiral out of control.
*This applies to anarcho-communism as well, which is essentially an oxymoron if such a system is meant to be enforced over any area larger than a small community. Barring a direct democracy making literally every decision about everything, a smaller group must manage the communally owned resources in a communist society (and if it's a communist society, everything MUST be "communally owned, or else;" otherwise, people will be free to be non-communists, and most people probably will...and it will no longer be a communist society). In order to
force "communal ownership" of every resource [or even every resource of a certain type] within a given spatial area, you cannot permit people to acquire similar private property of their own by any means. This means that you must enforce communism with coercive/violent force. Once the singular authority managing the use and access of resources obtains the power of coercive force and violence, it becomes the state, regardless of euphemisms that say otherwise.