Say, packing up all the politically problematic people is not an option, but leaving them behind is?
It is correct that the colony serving as an example here was founded for the purpose of feeding its riches back to the motherland but once it became independent, it started to drag colonists by sheer promise of opportunity.
As such, a space colony might not benefit earth (or a subsociety on earth) as a whole, at least not in economic terms, yet if enough humans see an opportunity in leaving earth behind, their benefit might be sufficient to make it happen.
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