Yes!! I think some of these conversations tend to leave out scale. 

Communism within a family? that can work beautifully; may even be the natural state of a family.

Socialism in a small tribe or commune. Lovely, especially if folks can leave freely

Either of those for a nation of hundreds of millions? disaster 

 Scale, yes. Socialism/Communism are, in some ways, natural forms of human association....ON A SMALL SCALE. These methods of organizing people can't scale (morally) across the myriad belief systems held by humans. 

 yes, exactly

small scale and voluntary