$5 says that these same people would complain about the fire alarms "being too loud" if they were to malfunction and go off in the middle of the night.
I can sometimes understand quiet zones such as Vine Street over in Decatur, AL where the crossing gets 50 trains a day and it's right next to a neighborhood, but if I ran a city with a busy main line going through it, I'd put a buffer of commercial and industrial buildings along it so people wouldn't complain about the train horns as much.
I don't understand the quiet zones that are in the middle of nowhere though.