The BBC physicist Brian Cox has theorised that the only reason we haven't encountered extra-terrestrial civilisations is because civilisations that reach a certain level of technological advancement (nuclear weapons etc) probably end up killing themselves off.
Humankind itself has come close to annihilating itself before now, most notably with the Cuban Missile Crisis of 1962. And climate change (caused in part by technology such as cars) looks likely to be catastrophic, too.
There are over 100,000,000,000 (100 billion) galaxies in the visible universe, so there's got to have been some life out there.