> Although authors like Sagan think that a spacefaring species would
> most likely be friendly, I do not think that will be/is always the
> case.
Yes. Seafaring nations sure weren't always friendly towards other
cultures, so why would this change when they get into space?
> Is there not the possibility that extremely hostile races would
> not destroy themselves? Instead they might have a sense that they are
> supreme and all other species should be subject to them or simply
> annihilated?
And then there's also the possibility that the visitor is not a race,
but a single (planet-sized?) entity. Maybe it's the only survivor of a
titanic battle between Powers. Or maybe it's a super-AI that turned
against its masters...If it's powerful enough, it can be as hostile as
it wants to be. No, benevolence is far from a sure thing when it comes
to extra-terrestrial life.