It has become increasingly clear in recent decades that technological progress advances exponentially, and taken to its logical conclusion this may imply that anything that is theoretically possible will eventually be possible in practice. Also, it seems probable that there is some possible action (or more likely, many such actions) which would lead to the elimination of all life in our known universe. Given these two assumptions, a sufficiently intelligent life form elsewhere in our universe might rationally decide that the best way to reduce this existential risk is to concentrate power into as few entities as possible. The situation seems analogous to the cold war arms race following World War II, during which some prominent U.S. scientists wanted to use the hydrogen bomb on Russia pre-emptively, not out of a sense of jingoism but out of a belief that a planet was safer if only one entity had the ability to destroy it. This seems to me a genuine risk at the galaxy or universe level, although there's probably not much we can do to mitigate the risk... we've been transmitting signals into outer space since the middle of the last century, so any sufficiently advanced intelligence in our neighborhood who wanted us eliminated probably already knows we're here.