A nice take-down linked below as to why alien invasions are extremely unlikely. Except …
… we know humans do goofy things.
… we know humans are more than happy to kick indigenous people to the curb in order to put up their luxury home (or hunt that rare critter, or put up a plantation) thousands of miles from where you would think it would make sense. And sometimes it doesn't make sense and the enterprise goes belly-up, but that doesn't undo the damage.
… we know humans hunt rare critters, difficult to find, to extinction for bizarre reasons (aphrodisiac rhino horns and tasty shark fin soup FTW!).
Assuming that (a) aliens are rational actors, and (b) we understand the economics of (highly hypothetical) interstellar travel and trade are both hugely awful assumptions. We're not rational actors, and we don't even understand our own economies or are able to predict accurately what new technological and scientific discoveries can do.
So … always watch the skies … #ddtb
Embedded Link
Blastr: Astronomer: 6 reasons why aliens would NEVER invade Earth