For my part, although I'm certainly not as well read as Lyx and Masked, from what I do know, I do believe there is alien life out there somewhere. Whether it has advanced to a level where it could travel here, I'm still very much open to debate about though.
Only the most obsolete kind of scientists still believe that there is no life outside of earth. Nearly everyone agrees that it is highly probable that there is lots of "green slime" (non-complex life) out there. So, the majority of scientists do already asume, that there is lots of life out there.
A slightly lower, but still high number, of scientists also things that in *recent time* (millions of years), it seems probable, that complex life has emerged elsewhere. Where things become highly uncertain however is when you come near those questions, which matter for cross-species interstellar society. All those question are centered around a core question: it doesn't matter if a million years before there was someone able to directly or indirecly contact us. It also doesnt matter if in a million years someone will be able to do that. Someone needs to be there NOW for this to be relevant to us:
1. Does it survive long enough to even be able to open communication with us? There are all kinds of bottlenecks and "evolutionary tests" which a species needs to solve, just to survive for longer than the blink of an eye in an astronomical sense.
2. Did complex life emerge since a long time, or is this something new in this galaxy? If it is something rather new, then was there even enough time for their electromagnetic signals to reach us?
3. Point "1" and "2" in relation to direct contact: did they evolve to the point where they are able to travel between starsystems? Was there even enough time to evolve to this point?
4. Regardless of the previous points: how habitable is a galaxy anyways? Which conditions must be met, for complex life to emerge and generally be able to survive? A galaxy is not as life-friendly as most people think - the areas which are life-friendly are just a fraction of the galaxy as a whole.
Oh, and as for aliens attacking us - we are much more probable to start a war. Can someone name just one single species on THIS planet, which we do respect? I mean, come on: we do not even accept that many of them are conscious beings. Well, then why should this be different for species, which are even more foreign, than those on our own planet? Going further down this path: We do not even respect slightly different cultures of our own species on this planet. We are total xenophobes. The "enemy" which people are seing in aliens, is an enemy in their own head. Some alien lifeform which is able to travel between starsystems must have already solved this flawed logic, just to be able to develop an interstellar society..... and if they did already solve it, then they have also understood, that we are totally uninteresting to them. Just like i understood, that most humans are uninteresting to me.
The bottom line is: fix your goddamn own mess, instead of looking elsewhere. No one is going to save or punish you, except of yourself. There is a wonderful system called causality, which makes certain that we need no gods and other uber-masters, because we ourselves are already doing the job, simply by actions and their consequences. Besides, the aliens and gods dont give a damn about you, as long as you're such a fuckup.