Well put! One quibble, the Chicxulub bolide was about six miles across, but a half-mile object would destroy civilization. This one is about 64 times bigger (in volume) than the Tunguska object, which flattened hundreds of square miles and left no apparent crater.
Sounds like the Tunguska object came apart in the atmosphere as an air burst, rather than any significant amount hitting the ground as a solid object.
This is something I've been curious about for a while, namely the tensile strength of the average asteroid. Is it a hard, solid object (like a rock) or a loose aggregate of dust, mainly held together by its own microgravity?
In other words, if you put a chunk of steel in its path, so that it hit at several miles-per-second, would the impact knock a chip off the asteroid, or would it explode a big chunk off?