Which begs the question of WHY the Federation is post-scarcity in the first place. We know in Voyager that replicators use more energy than actually cooking food, which is why they had replicator rations and had to put up with Neelix's cooking. Also, as
Sisko said in his Maquis speech, colony life was not like life on Earth. Remember that time when Riker was hitting on some colonist and the Crystaline Entity cock-blocked him by turning the entire colony into salt? Just before she died, she was talking about how they didn't even have a replicator set up or the creature comforts we usually see, which is why she invited him to have dinner in her tent. Or Picard's fake son, Jason Vigo, complaining about how hard life was for him on the frontier? Or Turkana IV?
The Federation is the positive version of the Imperium of Man. They colonize whatever planet they can get their hands on, are poorly defended ("We're the only ship in range."), then when they meet opposition to some minor race like the Shelliak or the Talarians or the Cardassians, they get into a small border war and sign some dumbass treaty that requires the Feds to pack up and leave. I suspect the early part of the 24th century up until TNG was the Feds aggressively expanding or "exploring" without having to worry about the Klingons or the Romulans checking them. The Fed-Cardassian treaty wasn't even the first of it's kind either,
like when Data had to evict a colony because of the Shelliak. Why would the Federation have such sloppy colonization laws?
1. Raw resources. Even in Encounter at Farpoint, free access to interstellar trade was considered a boon to a planet's economy. So much so that the Bandii were willing to enslave a space jellyfish for membership. While "money doesn't exist in the 24th century," trade most definitely does. Because this massive trade network exists, the people are Earth and the other Founding member homeworlds can delude themselves into thinking they live in a post-scarcity society.
2. To remove undesirables in their society. Your average Earth citizen is like Joseph Sisko or Jaresh Inyo, liberal-minded, friendly, and despises the national security state. What about people like Eddington or the Irish Nationalists in Up the Long Ladder or the genetically engineered people in The Masterpiece Society or the Navajo? They are "encouraged" to leave to set up their own colonies where they are not under many Federation laws and allowed self-governance until some treaty tells them otherwise. The Feds help set up colonies to keep these people from thinking about the Fed government's problems.
General Chang also has an excellent analysis of how the Federation actually functions @33:33
https://youtube.com/watch?v=XqVlSNP1jEI