They might have some sort of immigration quotas for the Earth, and if the population is approximately what it is now, then there's going to be a lot of open space, farmland, and wilderness still. That's assuming you have cities with a lot of people packed close together, and rural areas with sparse population. That seems much better than the alternative of turning the entire land-surface of the Earth into a uniform-density suburb.
There's a pretty big difference between being able to colonize the universe and being able to colonize planets near to you. As an example, the Federation wasn't even able to map out a single galaxy nevermind colonize it.
monkeybutton|4 years ago
CalRobert|4 years ago
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White_Wolf|4 years ago