The answers to this this question make it clear how modern airliners dump fuel in the case of an emergency. As far as I understand, fuel dumping might be done to lower an aircraft's weight to the maximum landing weight, particularly soon after takeoff.
As far as I understand, jet fuel is typically not safe. When I, as a complete outsider, hear of fuel dumping, I imagine a whole bunch of dangerous corrosive fuel being dropped on whatever happens to be below, and it sounds like a frankly awful idea.
What makes fuel dumping safe, or if it is dangerous what makes it worth it?