Bah. You kids these days...
Back in my day, we didn't complain about the cold and lack of oxygen. We rode in unpressurized planes with open gun ports. Sure, it was cold -- we wore fur lined jackets and liked it. Our oxygen masks smelled like engine exhaust and we were grateful. You didn't here us whine about 'being crushed by landing gear' or 'being thrown from the plane'. We were being shot at. Hell, we were lucky to have landing gear at all when we got back.
So, stop your bitching and get off my damn lawn.
Written for my grandfather who manned a gun in a WWII bomber.
Most science fiction says it happens this way:
After the asteroid impact... Humanity pulled itself from the breach of collapse and rebuilt. Once they could regain a foothold on space, they made it a priority to put in place the necessary resources to make sure it would never happen again.
OK, so, while it is fiction, sometimes literature provides insight into the human psyche. Frankly, I doubt you'll be able to convince the world governments to put any real money into an asteroid defense venture... that is until an impact happens and does sufficient damage to wake up all the people in power up. Most think that it will never happen. Most also believe they have more important issues to deal with in their local district and can't concern themselves with global issues.