Why does Hawking think that humans should never reply to alien radio signals?

If aliens can send a certain signal, it means that aliens have developed to a level similar to or even higher than that of earth civilization. Our earth civilization has not completely conquered and used the resources of this planet, and its resistance to alien intelligence (the impact of small celestial bodies) is very weak, that is, it lacks the ability to protect the earth. So how to face an alien civilization equal to or higher than the earth civilization? Besides, who can guarantee that alien civilization is peace-loving? Therefore, in the case that the earth civilization has not developed to a higher level, for the safety of the earth, it is best to avoid contact with alien civilizations as much as possible, and it is best to hide itself and develop silently.

(1) Hawking focuses on safety. Think about it. If humans reply to the signals of aliens, if aliens have the ability to come to the earth again, they can know that their technology is far higher than humans. And coming to the earth from a distance is most likely for their interests, such as wanting to use the earth as their base or a place for immigrants.

Because aliens have developed higher than our earth science, but human science is still developing. Thanks to Wukong.