This is something that few people are truly considering:
Besides the possibility of life on other planets (or moons), one must consider the possibility of what that life is.
As a general statement, the odds of it being anthropomorphic are slim and none. Do not forget that we were not a predestined result of evolution, mammals dominate the planet solely because meteoric impact annihilated the giant reptiles (i.e. dinosaurs) that previously dominated for dozens of millions of years. Apes haven't existed for even a blink in time compared to the time these creatures covered the globe. Also do not forget that our cerebral cortex is an evolution upon the reptilian brain structure, and that prior to their extinction, several species of dinosaurs evolved brain capacities that must have conferred intelligence similar to modern birds and perhaps even higher mammals (obviously not including humans). This, 65 million years ago. Had they not died they may have evolved much further, we will never know.
Reptiles themselves evolved to deal with the conditions of interior terrestrial existence, away from water.
Amphibians evolved to exploit existing resources on water fronts.
Terrestrial plants themselves were responsible for literally terraforming the entire planet, rendering it habitable in the sense we know today. Said plants took millions of years to actually colonize the interior land masses.
And so forth.
The odds of a planet having conditions suitable for any life are small (per planet; the odds of there actually existing other planets must be admittedly high given the number of planets likely existing in the universe, even if they are far outside our reach). The odds of said planet having conditions vaguely resembling earth are ridiculous.
Therefore, whatever life exists elsewhere will have evolved under very different circumstances and will almost certainly bear no particular resemblance to life on earth. The only requirement is that it is able to replicate itself, causing proliferation and evolution (yes, evolution is a foregone conclusion of any replicator capable of error in replication). These beings would not belong to any of the five kingdoms of life on earth, cladistically speaking; in other words, even if it is mobile, has a nervous system of some kind, and feeds on other beings, it is not an "animal." It's something else.
Therefore, questions about whether this life is "intelligent" or "peaceful" or whether it gives a shit at all are all moot. This life will almost certainly not have anything in common with us except replication and the presense of survival mechanisms. What those mechanisms are (intelligence, for example, is a survival mechanism), statistically speaking, is probably nothing we know much about.
However, given the general prevalence of xenophobia among earth life (most animals don't particularly care for members of other species and often not even members of their own species), if we are going to view aliens in earth terms, probably they won't like us much.
"The devil I'll bring you," answered Hagen. "I have enough to carry with my shield and breastplate; my helm is bright, the sword is in my hand, therefore I bring you naught."