I wrote in Libertarianism: A Primer, "One difference between libertarianism and socialism is that a socialist society can't tolerate groups of people practicing freedom, but a libertarian society can comfortably allow people to choose voluntary socialism." (In the final section, "Toward a Framework for Utopia.")
Now Ira Stoll notes the irony that it was very successful capitalists who put up the money that allowed Michael Moore to make his anti-market screed Capitalism: A Love Story:
The funniest moments of all in the movie, though, may just be in the opening and closing credits. We see that the movie is presented by "Paramount Vantage" in association with the Weinstein Company. Bob and Harvey Weinstein are listed as executive producers. If Mr. Moore appreciates any of the irony here he sure doesn't share it with viewers, but for those members of the audience who are in on the secret it's all kind of amusing. Paramount Vantage, after all, is controlled by Viacom, on whose board sit none other than Sumner Redstone and former Bear Stearns executive Ace Greenberg, who aren't exactly socialists. The Weinstein Company announced it was funded with a $490 million private placement in which Goldman Sachs advised. The press release announcing the deal quoted a Goldman spokesman saying, "We are very pleased to be a part of this exciting new venture and look forward to an ongoing relationship with The Weinstein Company."
So maybe I should add a corollary to my claim:
One difference between libertarianism and socialism is that a socialist society won't put up the money for people to make libertarian movies, but in a capitalist/libertarian society the capitalists are happy to put up the money for anti-capitalist movies.
And if you doubt that a socialist society would discriminate against anti-socialist movies, you can either observe socialism in practice — in Cuba, China, the Soviet Union, East Germany, etc. — or read the chilling words of bestselling economist Robert Heilbroner in Dissent:
Socialism...must depend for its economic direction on some form of planning, and for its culture on some form of commitment to the idea of a morally conscious collectivity...
If tradition cannot, and the market system should not, underpin the socialist order, we are left with some form of command as the necessary means for securing its continuance and adaptation. Indeed, that is what planning means...
The factories and stores and farms and shops of a socialist socioeconomic formation must be coordinated...and this coordination must entail obedience to a central plan...
The rights of individuals to their Millian liberties [are] directly opposed to the basic social commitment to a deliberately embraced collective moral goal... Under socialism, every dissenting voice raises a threat similar to that raised under a democracy by those who preach antidemocracy.