Enjoyed the article and I agree with your point generally; I do think that we need to spread out beyond our planet if we are to survive as a species. I like the story of the worm, did you know that part of the EU’s Human Brain Project is aiming to create a spiking neural network that simulates the human brain? They’ve more or less managed a mouse so far. :-)
However I think that your dimensions are a little bit off — 1000 foot is relatively tiny and on average asteroids that size hit the Earth once every 6–7000 years. They’d cause a crater of about 2-miles in diameter and an earthquake of about 6.8 on the Richter scale, which would be damaging but not quite extinction level. Slightly bigger than the Tunguska event in 1908. Something big enough to endanger humanity (or at least civilisation) would be at least 10000 feet in diameter, depending on rock density and velocity.
This impact calculator is fun, in a dark kind of way.
Amusingly I’ve heard that the risk of the impact of an asteroid capable of causing major damage to a city or infrastructure actually breaches the UK government’s public safety threshold for natural disasters, so in theory at least they should be trying to do something to stop it…