[njarboe]

I like the idea that when an old and powerful Galaxy ranging alien race discovers a planet that has life, they place that solar system off limits to any settlement and only observations are allowed. It does not seem that unlikely, unless life is just not rare at all. If 1 in 1000 or 1 in 100 or even 1 in 10 systems were set aside in this way, that would leave plenty of solar systems to continue to expand into.

In the US, we got rich and powerful enough around the 1880's that nature was basically conquered and we wanted to start preserving places for their natural beauty. By the 1970's we had set aside huge amounts of land for National Parks, State Parks and wilderness areas. Wilderness areas alone in the lower 48 is about 64.4 million acres, or about the same as cities and towns (urban areas are 69.4 million acres)[1].

[1]https://www.bloomberg.com/graphics/2018-us-land-use/