Whether we make it, or not, the human race has got to keep up its well-earned reputation for ferocity. If the slugs taught us anything, it was that the price of freedom is the willingness to do sudden battle, anywhere, any time, and with utter recklessness. If we did not learn that, well–“Dinosaurs, mover over! We are ready to become extinct.”

“Sam”
Page 338 “The Puppet Masters” by Robert A. Heinlein
[Excellent book. And I think the above quote applies to more than just invading aliens who wish to have us as slaves. There are lots of terrestrial predators than periodically need to be put in their place if we are to keep our freedom.–Joe]