And how are we to define what is parody -- ask the person parodied?
Nobody but Trump seems to be saying what South Park did is anything but protected speech for example.
Unfortunately, sometimes objectionable things are done with free speech -- we need to balance the harms to the many against the complaints of the few, and further... under my arguement you can simply not be a public figure if you don't want these sorts of things to happen.
It's well established that public figures have less rights around these matters.