If you aren't an independent adult, and you don't need or even shouldn't have unconditional digital freedom (no one's 8-year-old daughter needs unconditional digital freedom), a moon from someone else's planet is fine. (Even most of today's independent adults don't complain enough about being Facebook's moons.)
It's literally a bullet in their "objections" post.
I think your reading of that bit you quoted is extremely uncharitable. I don't see where urbit is passing pronouncements on anyone's "worthiness". The way I read that quote is, "an urbit planet is server software, and there are way less than 4B people with a server to run it on."
That's beside the point, though. Using scarcity to create value is not "extremely unconventional"; it's about the most ho-hum idea in Urbit. If you want a 128-bit address, you can use those in Urbit just fine. The only difference is that they don't have a default-positive reputation (where "reputation" is an abstract concept -- in practice, e.g. some channels wouldn't let 128-bit address post comments)
[0] https://www.census.gov/population/international/data/idb/wor...
Link? My understanding was that the official answer was "there should be about as many urbit addresses as adult humans so that they're too expensive to spam from, and if urbit is ever so wildly successful that we start running out, it won't be that hard to add more." (though I don't remember where I picked that up either)