I don't think banning cars is always a good idea (okay, secretly I do, but shh), but it should be seen as one policy choice not some sort of weird unpossible thing. I'd bet many more people travel down Madrid's Gran Via on foot or in buses or taxes than in private cars. Much of the that part of Madrid is either pedestrianized or effectively car-lite (not sure to what extent cars are banned or just heavily discouraged in various ways), though small delivery vehicles and similar can crawl through most places.
A lot of space once "owned" by pedestrians and transit riders was given over to private automobiles. Taking it back should continue to be a considered option where appropriate.