Why don't the three-body people in "Three-body" use Naoko to destroy mankind?

The specific reasons need to be analyzed, and the original work has not made a clear explanation. However, judging from various clues, Santi people don't really want to destroy the earth people. The original plan was to lock in fertility, and later it was to let the whole world immigrate to Australia. Perhaps the reason is that the Three Tribes are not a violent and greedy race, and invading the earth is also a prerequisite for the imminent destruction of their own planet. However, if we simply and rationally analyze Naoko's killing behavior in Australia, only by taking that kind of action at that time can we control the situation in the shortest time and avoid trampling or other riots. Of course, this is all my personal speculation. Of course, with the scientific and technological level of the three-body system, the earth people can definitely become extinct.

Secondly, some friends say that Naoko can hardly have an impact on the macro world. This answer is correct. However, this should be a bug in the original, and it is a serious injury. If it can't have an impact on the macro world, isn't that what Wang Miao sees from the macro world? Isn't the later Naoko robot the macro world? If not, how can Na Zhi control the robot? ...