Today is Asteroid Day, in honor of the June 30, 1908 Siberian Tunguska asteroid strike that hit with a force 1000 times the Hiroshima atomic bomb in the middle of nowhere. Objects falling to Earth from space, while rare, can be devastating when they do hit, leading to more than one of the mass extinctions in the history of life on Earth. We don't want to end up like the dinosaurs.
These are low probability, but immense consequences events, and we have finally reached a point technologically where we have the ability to identify potential threats and do something about them before it is too late. Even a comparatively minor strike, like the Tunguska event, would be a catastrophe of epic proportions it it hit an urban area. This is one kind of catastrophe we can't afford to learn from tragic experience from after that kind of hit.
A major investment in asteroid defense is well worth it, if it ever becomes necessary, and the probability that it will be invoked at least once or twice in the remaining history of human civilization is real. It will do more to make us safe than many comparable investments in national defense, and of course, it is a question of national (and global) security.
And, yes, there is an app to evaluate the risk.