“Theat way we can hunt ‘em down and kill ‘em before they kill us.”
Or you could read Cixin Liu’s Three Body Problem, Dark Forest (where that idea is explained), and the conclusion - Death’s End
Finally! Another freeper who has read Dark Forrest! Great book. Seriously thought provoking. There is probably just no way alien intelligence life would be a good thing for us. Yet we persist in thinking they would be benevolent.