I don't think so, and I really think authors, Hollywood directors and people in general are really missing the point when they talk/think/write about hostile aliens visiting Earth.
I mean, think about it: we (humans) are a very primitive, war-like species, and where has that gotten us in the space exploration game? Sure, we've sent some of our people to the moon (363K kilometers at its closest point), but that's merely six one-thousandths of the distance to Mars (at its closest point), and at that distance we've only been able to send a few bolt-buckets. Fantastic. So, with our war-like tendencies (even though we are still very early on in the evolutionary game), we barely have the technology to walk to the end of one block and back in our own solar system after, what, a couple thousand years of existence?
What's more, the technology needed to make inter-stellar travel even thinkable is so far away from us it's humorous. Some kind of space-warping propulsion system would be necessary (even traveling at light-speed would take way too long outside of the nearest star systems), and we can't even agree on the math that postulates its feasibility. Then we need to discover how to power such a propulsion system (nuclear energy isn't going to cut it, and we are just starting to figure out matter-antimatter collisions), figure out how to counteract the tissue degeneration humans go through in a zero-g environment (can we harness gravitons to create an Earth gravity analogue, or can we make centripetal exercise equipment work for the long-haul?), design and build the ships (who's paying for that? Certainly such an endeavor would wreck the world economy in its current configuration) and on and on and on with the things we can barely comprehend at our stage.
So, to do all of that and actually somewhat-master inter-stellar or inter-galactic travel, I'm positive that any species actually doing that stuff would have abandoned most (if not all) forms of armed conflict long before they were even capable of beginning the long road to that end. And murder, genocide, slavery and war would all be extremely primitive practices to them, and viewing us as a species would inspire "you guys still do that stuff?" kind of reactions.
Obviously I could go on and on about this subject (if anyone is intrigued, though I doubt it, I'd be happy to), but this post hits the high notes pretty well.
Good post; however, I disagree with a couple of your assertions.
First, "war", or any conflict with sybiosis, dramatically increases advancement. From microbial evolution to advances in human technology, battle/war/conflict forces adaptation (resistance through advancement), or extinction. This truth is fundemental to all earthly things; why would, or should, it be different for alien life?
I would contend that war is the ultimate boost-up for everything from medicine (war against desease) to communications (war against spacetime). My favorite recent example: we went from flying in paper covered sticks with a tiny motor to jet power in less than four decades because of war. Beep beeps on a telegraph wire to live streaming video wirelessly, on a handheld device, in less that two hundred years is a close second. War is neither good or bad, it's simply necessary for advancement. What alien wouldn't recognize that
Second, human beings are very far removed from "primitive".
In our current "modern human" form, now known to be on average about 98% homo sapien and 2% neandertal, we have only existed for about 100K years. See my first point.
In that extremely short period of time we have become the masters of all life on the entire planet, one that has harbored countless diverse lifeforms for billions of years. Even tracing our parent's parents back to when grandmother first climbed down from the tree and stretched her legs upright, we have only existed for a few million years; mere minutes by earth's clock and barely a discernible fraction of a second in the 14 billion years of the known universe. And we got to where and how we are so fast by killing, cooking and eating other creatures.
What do you bet aliens taste like chicken?
And so it goes that in a relatively short order we will know all things knowable, do all that is doable, and/or become extinct. Either way, we are probably about half way there, and far from primitive.
To the original question, are we alone? No.
As other posters have pointed out there is likely life on other planets and moons within our own solar system, and we now know our system is nothing out of the ordinary. Given the mathmatical probabilities, the universe is teeming with life.
But things get a little tricky looking for "intelligent" life; it isn't a question of where to look (goldilocks zones) but rather
when we are looking.
If you had happened past our planet a million years ago in your spaceship would you have thought it contained "intellegent life"? No.
If you were listening to Earth from your advanced alien SETI project 1000 years ago, or even 100, would you have detected intelligent life here? No.
We only started broadcasting our own existence in the last century and didn't start really screaming "We're here", until about 80 years ago; and now we are growing quiet again. That is a pretty short window of spacetime with which to notice even a nearby neighbor, assuming you are even listening for them during that specific time relative to your own in the first place. And how long have we been able to listen out for them? Hardly any time at all.
To really put things into perspective consider that nothing you see in the night sky is actually when/where you are seeing it, and the farther away from you that thing is, the longer gone it is from that place or time you perceive it to be.
Know that the star you look up at tonight might have gone nova a thousand years ago and really no longer exists; but the news of it's death hasn't reached us because the light of it's destruction is too slow to have overcome the distance yet.
The odds of life out there? A sure bet.
The odds of advanced life existing at the same time as us at a reachable distance even for radio waves? A long shot.
The odds of aliens visiting us from a star system 4 or more light years away to throw a probe in our ass? A sucker bet.
We aren't alone, but we probably might as well be. Time.
