Sorry friend but you seem to be misinformed. Please reduce your level of vitriol, especially given that your facts aren't quite right.

The extinction caused by an impacting meteorite is not related to directly getting hit. The biggest issue is that it kicks up so much dust that the atmosphere can lose its transparency. When less sunlight reaches the ground, plants can't thrive, and then we have a food crisis. Doesn't matter where it hits, everyone is affected. If it hits ocean, then we have tsunamis that destroy multiple coastal cities all at once.

Of course not every asteroid hits earth, but we don't know which ones are headed our way (or, more accurately, which ones have orbits which, factoring in uncertainty, may result in a conjunction with the orbit of the earth) until we find them and track them.

Having the moon is nice, but the moon isn't a magic vacuum cleaner. Asteroids have every capability of coming down. One killed the dinosaurs, one caused the Tunguska event, and one was in Chelyabinsk just a decade ago. Clearly the moon isn't sufficient to protect us. It orbits around so it only has an effect on one side of earth at a time.

The atmosphere is a joke compared to an extinction-level meteorite. The velocity is high enough to not be sufficiently slowed to a safe level, and the object's mass is sufficient to maintain integrity despite aerothermal ablation.

How would we know if we saw most of the asteroids? We don't know which ones we're missing because... we're missing them. And what makes you think that the top scientists are choosing asteroid-hunting as their science of choice? Why aren't the top scientists biologists, geologists, chemists, or anything else? How many organizations can you name which have a chief purpose of asteroid hunting?

What would it change? If we can detect asteroids early enough, then we can do something about them and prevent them from impacting us. That was the whole point of the DART mission last year. We took an asteroid that wasn't coming toward us, and deflected it into a different path, which was still not coming toward us. But it proved that we have the active, current, present technology to deflect an asteroid, presuming we can send a spacecraft to it soon enough. But we can only do that if we detect the asteroid and have enough time to deflect it onto a new course.

Please, chill a bit. This type of hostility won't win anyone over to your side. Have a nice day.