If what you care about are lives saved, then a massively expensive program to deflect Tunguska-class asterioids is *not* worth it.

Given the numbers involved, you'd do far more for humanity by putting tens of billions into malaria treatments, work against a number of other infectious diseases, seismic strengthening of buildings in earthquake zones, or installing airbags on Nanos and other cheap developing-world cars. Or if you prefer, building anti-ballistic missile systems to protect cities from equally devastating strikes by Iranian, N Korean, or whomeverean nuclear missiles.

Surveys to rule out a civilization-threatening impact are worth it -- and we've largely accomplished that (barring long period comets, for which we should keep a lookout). Certainly worth more money to finish the job and if we see something threatening coming within the next few centuries, it'll be worth big bucks to build deflection capabilities. THough if we have 200 years warning, I'd recommend we spend 20-50 years doing studies and technology development rather than a crash program that may be more expensive and less effective than if we use the time for major R&D first.

If surveys to rule out Tunguska-class impactors are reasonably cheap, then sure, keep them up too. If we're talking billions for them, or for actually building deflection capabilities today, then no. Many billions against once in 5,000 years, one major city being lost, is not worth it given competing risks and indeed certainties of deadly perils.