If we ever achieve some form of reasonable, in-system spaceflight, then we are really going to have to start worrying about every crazy person with a spaceship bumping a smallish space rock into an impact orbit with earth. Or even just unfortunate accidents. But it wouldn't take much of an asteroid to burn down through the atmosphere and create a Tunguska-level impact.

The most recent Expanse novel is an interesting take on how apocalyptic such an event could be http://amzn.to/2aD2AFl

Sprinting through Cibola Burn http://www.amazon.com/Cibola-Burn-Expanse-James-Corey/dp/031... before Nemesis Games gets here http://www.amazon.com/Nemesis-Games-Expanse-James-Corey/dp/0...

Also working my way through SICP to see if it makes be a better front end dev. Results pending.