Also, just to make explicit my hard-SFnal heresy on this point:
I do not believe that there is some inherent superfragility in space colonies that will require ZOMG FASCISM in order to keep everyone alive.
Manhattan has vital life-support infrastructure. We just don't *call* it life-support infrastructure. And if said infrastructure were to epic fail one day, you are almost certainly dramatically overestimating the number of Manhattanites likely to get out alive.
And yet somehow Manhattan manages not to be a quasi-paramilitarized authoritarian dystopia.
(Well, okay, but insofar as it _is_ an authoritarian dystopia - although non-paramilitarized despite the NYPD's best efforts - that has approximately nothing to do with infrastructure protection.)
tl;dr Basically, people are drastically underestimating the number of fragile points in today's Earthly world which, if lightly tickled in the wrong way, could kill people in very, very large numbers.
And yet we go on.
(Forgive me for not posting details of what I have come across in the course of writing research, since I am, quite reasonably, not entirely sure every reader of this toot is sane, safe, and consensual.)
@cerebrate Water supplies to desert cities are probably a biggie... Manhattan needs fresh water from somewhere too; I hear the Hudson is less drinkable than salt water.