After all, it might be that there are many more variations of evolutionary paths than the inverse of the probability of one getting this far... and who knows what a different evolutionary path for an ecosystem looks like? There is no reason our imaginations could be even remotely suited for such a task.
On the other hand, should we encounter sentient life, it certainly is not difficult to imagine hostility or callous indifference -- from either party. Particularly if said encounter is not on our terms.
And as profoundly exciting as the prospect of meeting alien life would be, I'd much rather it occur sometime after we've grown up a bit, ourselves.
Just because we can imagine something doesn't make it at all possible. We're speculating the probability of something having seen it occur once...
But now your also scared of storms :)
I certainly agree that our dataset, re: "life as we know it", is horribly limited. Likely to the point of uselessness. But hypotheses are the foundation of any science, after all, and what little we do have to go on suggests that competition/predation, rather than cooperation/symbiosis, may be a more reasonable expectation.
But perhaps not. In which case, we'd be very lucky to encounter such an enlightened species.