I'd like to have an optional sound. Using the horn is an act of aggression, but enabling a Jetsons-like sound when I want to alert pedestrians would be very useful.
You should be able to disable it. For example, when coming home and parking late at night (headlights are visible then and it is quiet so a sound causes pollution).
I have considered this as well. That is, setting aside the issue of electric noise vs. ICE noise, I think all cars should have two horn noises - the normal "horn" and a universally defined two-beep "friendly" horn.
That "friendly" horn would be very useful in many driving situations and would make many interactions less confusing / antagonistic.
So it is very important to have a universal class of sounds, and it must be forbidden to play sounds of that class on a street for other things.
I don't consider that cars should move faster than pedestrians in a city centre, so I won't change my behaviour if I'm already walking. However, it's useful to ask people standing to move to the side.