In a free society, groups of socialist-minded people would free to voluntarily experiment with socialism. They could congregate in some geographical area, and agree to donate their possessions to the community, and to share all produced goods according to some bylaws, or decisions of some elected or appointed governing body, etc.
However, the reverse is not true. In a socialist society, groups of free-market minded people would not be allowed to experiment with capitalism. Socialism requires, by its very definition, the surrendering the means of production to the collective.
In a world with copyright, content creators are still free to release their works to the commons, if they so desire. They might do so in hopes of increasing brand visibility, or in an altruistic desire to enhance culture with their entertainment or educational contribution.
However, the reverse is not true. In a world without copyright, content creators do not have the ability to exert control over their works. By whatever name, a society without copyright would entail the automatic surrender of intellectual capital goods to the commons.
So which model functions most like a free society, and which functions like socialism? The answer is clear: A world with copyright is like a free society, and a world without is like socialism. A world without copyright might properly be referred to as "intellectual socialism".