The destruction of all life is a much more threatening situation than simply that of humanity, though I'm not sure humanity would worry much past itself.

Since the protection of Earth from asteroids seems to be a two-part problem with the first part being relatively inexpensive, there seems to be a cost effective way to manage that threat.

It could well be that the cost of implementing an asteroid detection system would be miniscule compared to the damage which could be done. After a threat was detected and verified, then a determination as to how to deal with it could be made.

Given the urgency of the latter situation the resources of the world would open up.

As for selling the idea I believe it could be done as a by-product of a sexier idea, life on some Jovian moon, for instance, and an incredible bargain now that we were there. Another point could be that it would be possible to find a certain asteroid, the Rosetta Asteroid, which would contain the seeds of life itself if only enough of them were scanned. And that it would have to be small enough that some of it could survive in the atmosphere as it entered.

Just in thinking about this I've gone from regarding the whole idea as ridiculous to suspecting that the detection phase might be a good plan.

Arf