The fact is, Gene Roddenberry himself stated the Federation is intended to be a communism.
Well, since "a communism" isn't even grammatical, those obviously weren't his exact words. And I've been a Trek fan for nearly four decades and I've never heard of such a quote from Roddenberry. Can you provide a source to substantiate that claim, a direct quote from the man himself in which he uses that specific word to describe the Federation?
There's clearly no way an American television producer in the 1960s would've been able to get away with endorsing communism, and it's well-known that Roddenberry was quite a dedicated capitalist, doing whatever he could to make a profit off
Star Trek. And of course money and credits were frequently mentioned in TOS. The earliest mention of the Federation as a moneyless society was in
The Voyage Home, a film on which Roddenberry was nothing more than a consultant. It wasn't until TNG that any Roddenberry production started speaking in terms of humanity having outgrown the pursuit of wealth. But that alone does not equal communism. On the contrary, communism is very much about the pursuit of material wealth; it's simply that the material wealth is doled out to everyone. A system where people don't actually
need material wealth to survive is something entirely different from communism, something Marx never conceived of.
The difference, however, is it not supposed to be a communist society that has the same stigma attached to it when Russia and China attempted to force their countries to become communist societies, it was meant to be the type of communist society that Marx predicted the US and Europe would eventually evolve into.
It can't be communism of any kind because communism is an economic model predicated on scarcity and a labor-based economy. It therefore wouldn't work at all in a post-scarcity, replicator-based society. Yes, communism is
a non-capitalist system, but assuming it's the
only non-capitalist system that can ever exist is ridiculous. If nobody thought of communism until Marx and Engels came up with it, then doesn't it follow that there could be some other, entirely new economic theory that nobody has thought of yet but that people in the future will invent?
There is a huge stigma attached to the word "Communism" in the US without understanding the true underlining concepts. You can't have a true communism until society reaches as a whole reaches a point where anyone would offer help to anyone else who is in need and that person would never dream of taking advantage of it.
When China and Russia did it, they created a dictatorship and forced people to accept communism, but the drive for personal gain and personal possession above all others still rung as the default human characteristic from the top of the government all the way down to the bottom. If someone could take advantage of another, they sure as hell did (and do).
No actual communist nation has ever existed. The socialist states instituted by self-styled Communist parties were intended as part of a process moving toward the
eventual achievement of communism. Marx taught that a society must go through several phases, from agrarian feudalism to industrial capitalism to a socialist dictatorship that redistributes wealth and educates the populace so that the state can eventually dissolve itself and give way to a stateless communist utopia.
The fatal flaw in this, of course, is that it's tragically naive to think that any institution, once given absolute power, would be willing to work toward its own dissolution. That's why these societies always get stuck at the socialist dictatorship stage and never actually progress to true communism. Communism is the goal they're theoretically working toward, not the actual system they employ. (Also, Marx was dead wrong in his assumption that socialist revolutions would happen in industrial capitalist societies; most of them were in agrarian societies.)
Now you can go back in various series and point out various places where someone said "This cost that", but reality one of the looming problems Star Trek as a whole struggles from is not having a concrete of standards bible that everyone played from when writing for the series.
Again, the absence of money does not equal communism, because "communism" does not mean "everything that isn't capitalism." A post-scarcity civilization would have to be based on a
new economic theory, not a relic from the 19th century.