Is a vast, utopian enterprise like PanGaia realistic?
Yes, and inevitable.
General Objections:
These are all addressed here.
Population growth occurs when the human enterprise is trying to solve a problem which is otherwise unknown or being neglected (that is, where new lives come into existence to deal with the undealt-with problems their parents made). Address your ancestral Karma and watch the drive to create babies go away (as well as your world becoming more beautiful and conflict-free...)
Governments ultimately have to answer to their principles and ideals in order to sustain themselves. At some level karmic consequences to "removing" people are perceived. If your government is oppressive, get (documentedly) arrested and bring it to the attention of the people and supreme courts, where issues of principles and values are determined. No dictator can stand long acting on arbitrary whims of power and even among systematic, dark deeds of oppression -- the human spirit ultimately must and will break free owing to the fact that any economic system is dependent on new-value creation -- and creativity requires freedom.
Complexity? Well that's the solution I'm answering and offering here.
Please talk to me more if you have doubts....