Earlier quoted context omitted.
The time to initiate an asteroid defense project is long before a threat is even detected. There needs to be time for technology development, deployment, and testing. Tackling an extinction-level event is not something we want to scramble for at the last possible minute, using untried technology.
> Tackling an extinction-level event is not something we want to scramble for at the last possible minute I am not sure if this is in line with Agile principles like YAGNI.
It's hard to estimate how long it takes for another humanity to develop if we screw it(so we don't know iteration length), and there is the problem of telling them what we did wrong after we were destroyed.