Stephen Hawking has come out with a strong caution against trying to contact space aliens. In Stephen Hawking's universe the likely put us on the wrong end of the same scenario where the white man who ultimately over-ran the Native American population. The reasoning is simple, those with the technology to achieve such transit (like the Europeans across the Atlantic), would also have the capacity to soundly defeat us, the backwards people still dependent and living off of the earth's bounty. With such an opportunity, why wouldn't they just take what they want?
Dafydd ab Hugh, co-author of the Doom Novels has the most pragmatic reply. He takes a number of well (if not over-written) scenarios of war-like aliens and shows how completely infeasible it is. He then notes that he's struggled with this before in his own writings...
When my pal and worthy co-conspirator Brad Linaweaver and I wrote the Doom tetralogy, we wanted (for plot reasons) to have an interstellar war (we were writing a subluminous, Einsteinian space opera, which I think is unique in science-fiction history). My goodness, how we struggled to come up with a reason that was not preposterous on its face, that was vaguely plausible, why alien races would ever go to war!
We finally settled on a long-ago dispute between competing schools of literary theory, the Surrealists and the Post-Modernists, each trying to analyze a fistful of fragments left behind by the first race ever to achieve spaceflight, billions of years earlier. These academic disputes erupted into a war that, due to lightspeed limitations, still continued after thousands of millennia. But that took us days of teleconferences to concoct.
Simply put, logic implies there is simply no reason for beings of one stellar system to attack beings of another. And while it's true that alien logic might be very different, we don't have any to study; so we're stuck with our own logic. To be frightened of the prospect of contacting aliens is to yield to xenophobia and the mortal sin (and bleak helplessness) of despair.
But he left one flagon unfilled though he set it at the table. Perhaps this flagon was a bit strong on the philosophy in a pragmatic menu of the logistics of inter-stellar war
The Klingons were a war like race, ready to exploit anyone and everything around them. The Federation stood in ideological opposition, helping each society grow on their own. The Federation even instituted a Prime Directive that was ultimately an act of discipline, don't deal with undeveloped societies at all.
Watching the struggle between the two, the same question kept coming up. Could Klingons, with their sense of warlike domination, ever have developed the technology needed without killing each other first? Would any race that learns the skills of domination and exploitation not even more become their own demise of undermining the very source of their livelyhood when they learn to harness power capable of wiping out entire continents or planets? The Cold War was a reaction, a reaction of discipline, in light of the creation of a weapon that could wipe out the earth. Could they have cooled off their warfare?
The game theory of confrontation is also simple. Where the threat of being exploited exists, it is better to be on the side of being the exploiter. As General Patton put it, it is better to get them to die for their country then for you to die for your country. He also noted that a poor plan executed violently will prevail over a superior strategy.
But the ability to exploit with greater power comes with the danger of undermining your own ability to tap resources. Today is the anniversary of the Chernobyl disaster, which was by no means was an act of war. It wasn't even an act of natural exploitation. It was simply a failure to implement the safety required for handling the worst case scenarios of nuclear power. If anything it was a failure to act, it was a failure to enact discipline. Discipline, the ability to enact safeguards even when no danger is immediately present but still potentially dangerous, is the core of morality.
The Federation, the only political power in the Star Trek universe that is projected from a real history -- our own -- developed a sense of morality from the threat of unnatural disaster after another. After years of war, dark ages, and general strife, the society matured to note the power of morality was an essential survival tactic. Without great restraint and morality, there was no safety from great power.
Ultimately, however, that doesn't predict whether or not we can guarantee any alien intelligence we contact is benign. Because there is no guarantee that technology doesn't fall into the wrong hands. IIRC, the Klingons did not develop inter-stellar travel on their own, but took it from the Romulans who though war-like were very calculating about its execution. Their own isolationism kept them restrained, as opposed to the expansionism of the Klingons. But should an atom bomb fall into the hands of an aggressive society, wouldn't they still cut their own thoughts with it rather then realize its potential to send them to the stars? I don't know. But the question keeps coming up.