Given that any system capable of preventing an asteroid impact must, of necessity be capable of causing an asteroid impact, one should also factor in the possibility of governments involved using the technology provided for other purposes, and the probable desirability of those purposes.
Number of governments known to use public power reprehensibly in all cases during recorded human history? Greater than one.
Number of asteroid impacts known to have caused mass deaths on Earth during that same period? Less than one.
Tris
“The people have always some champion whom they set over them and nurse into greatness…This and no other is the root from which a tyrant springs; when he first appears he is a protector.” ~ Plato ~
