Swift's US adult fan base ... is unafraid to "go low"
The fan base is very large and in any group of that size there are going to be enough people willing to "go low" to form a mob. That doesn't mean that the average Swift fan is more willing to "go low" than the average person who isn't her fan. (I'm pretty sure that the average Swift fan is less willing to "go low" than the average Trump supporter.)