But what is the reasonable precaution here? You say "Much Bigger Rockets" a few posts ago but what do you do with them? Do you build them and just leave them sitting around and hope we can knock an asteroid out of the sky with one? If instead we build the capability to detect all killer asteroids 20 years out (which seems reasonable with today's technology (it will be expensive, but less so than our wars)) then we would have 10 years to build a big rocket and get it to an asteroid and give it a tiny nudge, and a tiny nudge would be all it takes if you do it when the asteroid is still 10 years away. A detection network probably involves an array of space based telescopes and supercomputers to crunch the data, and we probably get a lot of good side uses out of that. There are lots of good side uses for big rockets too, but they don't help you deflect asteroids if you can't detect them years in advance.
Also regarding you comment on lightning and shark attacks, those kill individuals, not humanity. Big difference.