The smart thing to do would be to id asteroids that can be eliminated well in advance of coming anywhere near Earth, by diverting them into the Sun or some other planet’s gravitational field. Then you don’t need to worry that they might pay us a visit some day.
I'm sorry but, that's racist and discriminatory of you! These are simply "undocumented moons" looking for a home orbit... You can't ask them for ID, and you can't deflect them away unless and until they break a law, or vaporize a continent. They'll probably claim political asylum anyway, I hear there is a lot of gang activity out in the 'belt. You know, the carbonaceous don't get along well with the silicaceous, and no-one likes the metalics...
Indeed, but just how do you propose to do that?