@Schneidend I thought that a lot of them were based around real-world philosophical or political concepts. Free League being Libertarians, Xaositechts being Anarchists, Dustmen being akin to some Gnostic belief systems and so forth.
Admittedly not all, and a lot were based around fairly niche ideas, but arguably they're closer to the real world than FR organisations.
The Free League has less to do with libertarians and more to do with just not wanting to get involved in the big debate of who has the right answers. The factions' main line of division is what they think the nature of the multiverse is. It's much more fantastical than the political ideas you have mentioned, though it's certainly possible the Sigil factions were based loosely on their principles.
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Admittedly not all, and a lot were based around fairly niche ideas, but arguably they're closer to the real world than FR organisations.