If you're serious about "ethical problems" letting our species of killer apes off of our home planet, how exactly do you propose to stop it? (Remember: Once you try it, you've just made these killer apes very mad at you.) Seems tricky, once the economics line up for space, unless you're talking mass genocide or mandatory doses of soma.
Transcending the millions of years of evolution that turned us into killer apes is the task of civilization and culture. But the megadeaths of the last century caused by wars between democratic governments actually dwarfed the prior century's wars between non-democratic governments. Maybe, to go back to the upthread discussion, there are better alternatives that don't involve the straw man of "isolat[ing] from each other as thoroughly as we can."