Ah ha, didn't have to wait long for "we've not tried real communism yet".
The reason for it, in my opinion, stems from the origin: in an ideal world, the whole population would agree the system is fantastic and introduce it, based on mutual respect. What actually happens is that crowds get furious and start killing and introduce a new system by violence, so it's hard to expect a nice fruit from a rotten seed.
As Aleksandr Solzhenitsyn put it:
Ideology—that is what gives evildoing its long-sought justification and gives the evildoer the necessary steadfastness and determination. That is the social theory which helps to make his acts seem good instead of bad in his own and others’ eyes, so that he won’t hear reproaches and curses but will receive praise and honors.
What obscures matters is that evil tends to operate in layers with each layer deceived by the layer above it in the hierarchy (or below it, if you prefer a lowerarchy). So at the bottom there is a multitude of relatively decent people who don't want to kill and really do believe in the system.
Anyway next time you experiment with utopias, try not to bring along hundreds of millions of unwilling participants.
A correction: most humans. There are a few who like communism. Why not them live their lives as they want? Communities like the Longo Maï are a living proof this is absolutely possible on a tiny scale when a willing subset is involved.
Because those people then starting to kill all the problematic people, as we saw in Soviet and China. They put all the blame on these "bad people" and sent them to the gulag.
You can't ever let people with this kind of thinking into power.
> Communities like the Longo Maï are a living proof this is absolutely possible on a tiny scale when a willing subset is involved.
At that tiny scale they depend on the surrounding capitalist people and therefore it makes sense they also abide by the laws of the country.