>Is it absolutely essential that people
>believe in the fictional concept of "property rights" in order to
>interact productively and peacefully?
In the real world, yes. Numerous groups have tried to eliminate property rights to create this wonderful utopia, and have pretty well proven that it's impossible. Communism works in small family/tribal groups, but fails horribly when attempted on a large scale. At the same time, trying to create property rights where they can't reasonably exist -- e.g. copyright on electronic media -- fails almost as badly.