On Thu, 16 Feb 2017 14:19:38 -0500, Davoud wrote:

An event that hasn't happened in human history
is unlikely to get people fired up to spend a $trillion or so for a
detection and defense system. Tunguska doesn't count; "nobody" knows
about it.

True enough. But let it happen just once and see how much money we'll
throw at it. We're very good at dealing (or attempting to deal) with
foreseeable problems once the actually bite us.

I believe that Clarke's novel _Rendezvous with Rama_ started with a
good chunk of Italy being destroyed by a small asteroid, resulting in
the development of an asteroid detection system that ended up
detecting an incoming spacecraft instead (that spacecraft having been
fashioned from an asteroid, however).