The best explanation is that the Haung He river bring great floods which destroys many of the cities around it, which is why it is called China's Sorrow
According, to the narrator bats while being treated as the sign of blood sucking entities they only haunt down other beings when they sense for survival reasons and on the hands we humans treat bats as the beings with the thirst for blood and destroying various fields or farms of natural resources. Along, with that some of the superstition also treat bats as more influential in the process of witchcraft leading its importance in all the dark actions that human can imagine about.
But, being a bat is way more better rather then being a human of evil nature because the narrator say's that then we will be considered more frighting then any other beast as we will then hurt some one feelings and will treat other people badly by doing things in a more improper way.And that is why the narrator prefers to be a bat rather then being a human of evil nature.
