What is the source of the human (and other species?) need (is it real?) to develop weapons? Understanding this may be important to making estimates of what we may expect from any aliens.
IMHO, most discussion on ET/aliens/etc is mostly just projection of the writers' own fears, hopes, and desires. Much of the popular literature on UFO aliens (including such films as Indepenence Day) is pure projection unleavened by even the slightest trace of biology or economics (lots of flashy hi-tech of course). At the risk of incurring the ire of a goodly number of PF readers, even the great Carl Sagan had a few scientific blind spots, in the sense that he appears not to have availed himself of some hard-won scientific results from biology.
ET as a branch of human psychology?