I think history has romanticized car-less cities. Horses spook easily, and kill people in the process. Massive quantities of animal feces and dead animal remains would overwhelm the minimal city waste-cleanup services. The constant sound of horseshoes on non-dirt roads is worse than normal car noise. Cars solved real problems of city life.
I think a better argument is that 'everyone' has a car, but in old cities, far from 'everyone' had a horse - they were for businesses or the wealthy only.
