Alien psychology - there's no subject with more unknowns. Who could say what a truly
alien species would think of us, or want from us? Anything we imagine is still limited by our own psychology.
If we're ever visited by anything extraterrestrial, it would most likely (IMHO) be something like the Voyager
probes. At best it might be a pseudo-intelligent probe, but almost certainly still limited to lightspeed communcations. Therefore anything that stumbles over us can't be an immediate threat, because it would take time for signals from the probe to reach the homeworld, and still longer for the invasion fleet to arrive.
Still, if an alien species came here, who knows what they might want? Maybe they would turn Earth and the other terrestrial planets and moons into computronium
, with or without our consent. If they think it's for our own good, how would we stop them?
It's an interesting scenario, but the physical laws of the universe are going to keep us safe from aliens, and them from us.