I find it somewhat surprising that supposedly informed astronomers act so "confused" about this issue. It seems fairly simple to me that we face a portfolio of threats...
* Some from larger (brighter) NEOs that can be tracked and forecast DECADES in advance. We've gotten much better detecting these puppies over the last 10 years using CCD scopes.
* Some from smaller (fainter), or closer to the Sun NEOs that can cause devastation with short warning times. These guys are fainter and rarely found with present detection HW.
* Some from those pesky comets swooping in on fast hyperbolic orbits, the nastiest ones coming at us unexpectedly from behind the Sun
...and so on.

Perhaps it's just an acedemic battle for funding of a particular search strategy.

If some wealthy altruist REALLY wishes to be a saviour of manking, they'll put their 10s of millions into a faint NEO telescope array.
Why this threat mitigation is not the job of a country's Department of Defense trully baffles me.

-p