I would have to agree with Pale Wolf that it's SS's idea of Utopia.
A). I'd give you two or three good quotations that make it perfectly clear that Usagi won't ever force her point of view on anybody, but I currently do not have the series easily accessible.
B). Who said it was Utopia? All we see is either a view of the city from a great distance or a devastated ruins of it from inside.
C). Our modern society is definitely not an utopia. But look at with the eyes of some man from the Dark Age, with its constant wars, poverty, no medicine, no human rights... How'd *he* see it, as not an Utopia?.. In short, everything is relative.
D). What I gather from the manga is that Senshi are basically the gods of the SM universe. There are no Yggdrasil, no gods or demons, just the Galactic cauldron and the Senshi instead.
Compare: higher level D&D cleric can resurrect up to 6 dead people in one swoop. Neo-Serenity can resurrect 6.000.000.000.
Don't you think that she could just have re-created the humankind as she saw it?..
Or even better, the Great Freeze was in fact the Judgement Day, and the Crystal Tokyo is the celestial realm (or how is it called in English) that Jesus promised all the just to rise in?..
Something along these lines, please, considering how much power is at work.