Let’s say I decide I’ve had enough with this whole Federation business and that humanity would be better represented by a Starfleet that follows my particular ideology. Assuming I could get enough people for crew and support, why can’t I start my own Starfleet?
I could replicate ship parts until I have a couple vessels. Go to new worlds and present myself as the official first contact of humanity. I could fly to Vulcan or Bajor and tell them no actually my organization represents humanity.
What’s going to stop me?
Just because it’s post scarcity and money is not pursued is not enough. You still need significant economic activity to put everything together, and big part of that is human labor.
About representing humanity that’s a politics side, does most of humanity recognize you? Piss off the federation president and get sent to found your own colony where you get to represent.