"Right now Mankind's main priorities are in inventing weapons and finding most ingenious ways to kill each other."

This comment is absurd. There are, what, maybe 100,000 people in the entire world right now actively working on creating new weapons. Certainly less than 1/1000 of the population. This has hardly been a priority of mankind since the atom bomb - far more people are directly involved with preventing climate change. Most people are pretty forward thinking.

As far as preparing for a meteor/comet collision with Earth, we would definitely need to see an imminent threat before we really started making progress. If we got a first-hand look at a significant collision with Mars and were able to document just how catastrophic it is to the planet, I definitely think more attention would be paid to preparing for a similar situation on Earth.