Unfortunately this technology is likely to be weaponized at some point in the future as radiation-free multi-megaton munition. The project name does tell us that the goal is to redirection not destruction of the asteroid.
This munition is very rare, has to be aimed a very long time before it can hit anything and the whole process is very noticeable. I wouldn't lose any sleep about that.
Counterpoint: it would, reciprocally, take months to launch a military strike to disable a military asteroid base, so it offers robust second-strike capability. You can no longer launch a sneak attack on your enemy's strategic bases.
The short timescale of nuclear war decision-making is chaotic, destabilizing, and has almost led to *accidental* apocalypse several times in the 20th century. Slow, deliberated deterrence could take uncertainty and accident out of the equation.
It's a good hypothesis that humanity developing asteroid deflection is more dangerous than not; that the optimal course is to do nothing.
(Fortunately, kinetic impactors like this project are borderline useless/harmless anyway (other than as basic research). Sagan was writing from the more ambitious worldview of the 20th century; a world where, if an asteroid is a problem, you cut a straight line through the problem with nuclear weapons. That's a more hazardous toolset!)
I think you might be overlooking the fact that it's simply a lot easier to redirect a big object than it is to completely destroy it. If the cheaper option does the job of keeping our planet safe, why would we try to go with an exponentially more expensive one?
