"I'd like to have an optional sound. Using the horn is an act of aggression ..."

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.