Splitting my response into two comments. > any civilization which could peacefully colonize a galaxy is not the kind of civilization that would colonize the ga

Splitting my response into two comments. > any civilization which could peacefully colonize a galaxy is not the kind of civilization that would colonize the galaxy at all. The very act of wanting to colonize self-selects for violence/exploitation. This isn't necessarily true. Colonizing is simply the act of moving to a different piece of land. Violence and exploitation occurs when colonists are engaged in resource competition. It's not hard to imagine that, given high enough levels of technological development and the overall size of the universe, a colonizing civilisation can pre-select and coexist with existing occupants. To put it another way, two hundred years ago, if I wanted to move a bunch of Europeans to what are now Addis Ababa or Bangkok, I would have to "colonize" the area. Now, all I would have to do is buy (multiple) apartments, or a plot of land or two and build a gated retirement community.