That would be the safest and easiest potential to imagine, but have you thought that all the Doomsday alien movies indicate to us and our ecosystems supporters so to speak, the greater likelihood and potential for armed conflict when or if we were to come into contact with another intelligent alien species?
One is preferable, however unlikely, the rest of the movies and imaginary scenarios tell us that we've a greater likelihood of it not being the case.
More than likely a case of the best defense simply being to avoid offense, but to continue to contain or ahem farm us, almost like pets lol