Let's worry about an asteroid that is the size of NY!!
How long would they have to bitch and moan and tell us they told us so if they found a planet killer?
An unforeseen rock that size could easily be interpreted as a nuke first-strike, that’s why, and google ‘US crater lakes’ to get an idea of the damage they do.
The Chelyabinsk meteor was about 60 feet, and (fortunately) it was still high in the atmosphere when it exploded.
Here’s a article about 150 feet of asteroid:
What If Friday’s Flyby Asteroid Hit Earth?
By Stephanie Pappas, Live Science Contributor | February 12, 2013 07:33am ET
“On Friday (Feb. 15), an asteroid half the length of a football field will buzz close by Earth. It won’t hit the planet, but if it did, the collision would create an impact large enough to level 80 million trees — or the entire city of Washington, D.C., and its suburbs.”
see also: https://en.wikipedia.org/wiki/Impact_event#Frequency_and_risk
“Asteroids with a diameter of 7 meters enter the atmosphere about every 5 years with as much kinetic energy as the atomic bomb dropped on Hiroshima (approximately 16 kilotons of TNT), but the air burst is reduced to just 5 kilotons.[7] These ordinarily explode in the upper atmosphere and most or all of the solids are vaporized.[9] However, asteroids with a diameter of 20 m (66 ft), and which strike Earth approximately twice every century, produce more powerful airbursts. The 2013 Chelyabinsk meteor was estimated to be about 20 m in diameter with an airburst of around 500 kilotons, an explosion 30 times the one over Hiroshima. Much larger objects may impact the solid earth and create a crater.”