We can't just give potential predators benefit of the doubt. I have no doubt that we COULD interact with other lifeforms peacefully, I'm just saying that "optimism" isn't really the best approach from a simple survival standpoint. I would suggest more of an "expect the worst, hope for the best" approach. Even if you were to go with the assumption that it's unlikely that extraterrestrial life would be inclined towards violence rather than peace, we're still better off preparing for the unlikely event that they are violent. Like Hawking said, "We only have to look at ourselves for proof that extremely unlikely things can and do happen all of the time."

I mean, if we prepare for the worst, our asses are covered. If extraterrestrials do end up being peaceful, awesome! We still have the means to protect ourselves if they aren't.

I'll throw another wise adage out there: "Better to have it and not need it than need it and not have it."