In a recent comment John Hunt mentioned the most probable solution to the Fermi Paradox and as more and more planets are discovered this solution becomes ever more troubling.
Whether civilizations are rare due to comet and asteroid impacts- as Ed Lu recently stated was a possibility- or they self-destruct due to technology, the greater danger is found in human complacency and greed. We have the ability right now, perhaps as hundreds or even thousands of other civilizations had, to defend ourselves from the external and internal threats to our survival. Somewhat like salmon swimming upstream, it may not be life itself that is rare- it may be intelligent life that survives for any length of time that is almost non-existent.
The answer is in space. The resources necessary to leave Earth and establish off world colonies are available- but there is no cheap. Space travel is inherently expensive. Yet we spend billions on geopolitical power games threatening other human beings with supersonic fighters and robot missile assassins. The technology to defend civilization as a whole from the plausible threat represented by this “Great Silence” will cost us no more than what we spend on expensive projects like vertical take-off stealth fighters and hyper-velocity naval rail guns. But it is not the easy money of weapons; it is the hard money of vehicles and systems that must work far from Earth that is unattractive to the corporate profit motive.
Atomic spaceships capable of transporting colonists and intercepting impact threats are the prerequisites to safeguarding our species.