The fact that the Star Trek community is based on a united federation is really just a side part of the series. The main focus of the series is usually encounters with other species and how the crew comes together to solve puzzling problems. Star Trek is not a political statement... It just so happens that utilities like the replicator and the federation allow them to add to the setting of what a futuristic community might look like. Besides, on a a universal scale, the federation is a small group of the human species engaging in trade and communication with other species in a more capitalistic universe. Capitalism right now is for profit but in the future it could be for technology and knowledge.