Unless somebody in the universe manages faster-than-light travel and communications, even if aliens exist (which is reasonable) we'll likely die out before we ever meet them.
Seriously, think about it. Alpha Centauri (that's what it's called, right?) is something like four light-years away from Earth. If we can accelerate a ship to one-tenth the speed of light (which is still roughly 30,000,000 m/s -- a RIDICULOUS speed), it'll still take forty years to get there. An entire generation will have passed by the time said ship makes it and another four years after that before we hear about it. You also have to figure out how to power a ship for that period of time... find a good place to land the thing... worry about getting people back... find a way to communicate on a four-year lag... get enough people together willing to leave the planet FOREVER (likely leaving their friends and families behind)... basically, resolve a total logistic nightmare. And even then that's just Alpha Centauri, the closest star to our solar system. There's likely not even life there. And even if we detect life somewhere, we have to get there before they develop nukes and potentially wipe themselves out like we always seem to be about to do.
"But what if they come to us?" They'll face the same problems.
tl;dr unless we find a feasible way to both travel and communicate at speeds MUCH faster than light, or an alien civilization does, we won't make contact with extraterrestrial life unless there's some hiding in our solar system we just haven't found yet.
I don't, however, agree with the aliens-avoid-us-because-we're-barbaric explanation. Most of us are generally reasonable people (from our perspective--we have no clue about extraterrestrial cultures, after all) that I'm sure they could share a few pro-tips with to fix some of our biggest problems.