To believe we'd be alone is the same as thinking we're the centre of everything but we quickly noticed that the sun does not revolve around the earth.
After all there is more than one Galaxy. As far as we know the space doesn't even have an end or at least it hasn't been found 'till now so what do we know about the darkest depths of space?
There could be an Eden-like place out there, there could be hostile species, hell there could even be humans! There could be another planet much like ours because we do not know, we can't possible know.
But things you don't know, you don't see, it doesn't mean they don't exist, it just means you can't prove it.
oh well, nobody states that they are planing or they want to attack us for sure, but there is something that is true: no being is perfect or pure kind angels, no mater how intelligent they are, there will always be good and not so good beings everywhere. If humans could travel to other planets, be sure that we would go there to take resources and/or investigating and/or experimenting with the flora and fauna we could find there just out curiousity.
I do believe that there is some form of life out there, but who's to say that they are close? That they can observe us? That they are more or even as advanced as us? If there is extra-terrestrial life, it could just be basic life forms, rather than intelligent beings like ourselves. And in terms of travel, would they even be bothered to come to earth (other than reconnaisance, in which case they wouldn't act hostile)? The only reason we should be concerned is if there was some sort of exodus to Earth because there planet is no longer as hospitable, but even then that would include a hefty journey. And that's assuming that these beings function in the same way as us, that Earth can actually support their life.
there are other kind of comunications that are not english XD 50 years ago paople who worked in project SETI created and launched a MATHEMATICAL welcoming message from Earth to all the space (I personally think it was SO wrong thing)