If car horns were only half as loud to the honking driver, protected in his glass cage, as they are to a person standing unprotected next to the car, honking would not be much of an issue...
There are some problems in life where a punch in the mouth seems like the only viable solution.
Comparing it to talking/texting on a mobile phone while driving, where the penalties are moderate and there is some enforcement, attitudes are changing - very slowly though.
I don't think most people know it is illegal.