Are there really more disadvantages..

Do you mean number of advantages/disadvantages, or magnitude? Communal-based sounds good, and has been successful in small, tight-knit groups where everyone has a common goal. Once those criteria break down, communal living fails. If it gets too populous, it's difficult to know everyone and therefore less likely individuals want to support folks they don't know. If folks don't have a common goal, they end up working against each other (intentionally or not) and the community breaks down. Plus, in large communities, it can become impracticle as it is difficult to know whether or not each individual is contributing to the whole.

I can't think of any of the utopian communities that have really worked well, over time. Are we talking about communist countries, or what?

I was thinking of the Amish (although I don't know much about them. There is also a similar group in back-woods Montana that have been around a long time.

I did forget to mention that isolation of the group from the outside world, allowing contact with the outside world only under controlled conditions seems necessary to keep the group cohesive.