It's not theoretical; you're just stuck in the unimaginative windshield perspective. We didn't build up our current situation overnight, and we could certainly work to undo it with proper zoning and time. Plus, there are a lot of people who do live in cities, but have to rely on cars because we've made choices that make cities car-friendly and car necessary. We're not going to eliminate all cars, but since most car trips are under 10 miles, maybe it's time to reevaluate how we get around for most of them, particularly in urban and suburban areas.