That's a great (and long) thread. Reminds me of a pet theory I have: that the post-scarcity utopia of the Federation is based on expansionism, and not sustainable.
They've managed to turn Earth into a paradise and give (mostly) everyone great life quality, but they did this by doubling down on exponential growth, which manifests in the constant need to get more and more planets to join the Federation.
You can see the expansionist vibes all over the show, and they've even been hinted at by various aliens in DS9 (although without any mention of economic implications).
I really think this is right, it would be nice to have a Star Trek like sci fi series that actually tried to tackle the issues. As a series it's been a source of inspiration for decades. It's a shame modern Star Trek is just generic sci-fi drama.
That thread points out some interesting observations about typical Star Trek inconsistencies (another one would be to think about why someone should move to a colony in the first place or rather about why not everyone can simply travel between planets as they like). But the objection against desalination is pointless. We can manage that problem already today (e.g., by drying up the brine or by pumping it into old oil wells). There is absolutely no reason to assume water would be scarce in the 24th century of TNG.
They might have some sort of immigration quotas for the Earth, and if the population is approximately what it is now, then there's going to be a lot of open space, farmland, and wilderness still. That's assuming you have cities with a lot of people packed close together, and rural areas with sparse population. That seems much better than the alternative of turning the entire land-surface of the Earth into a uniform-density suburb.