"Cars should merely be one use of the roadways" is equivalent to "people who can't afford decent urban homes should live in shitty urban homes." The primacy of the car is what lets us currently live in decent suburban homes.

Urban and suburban residents have competing interests here: urban residents (for whom cars are a nuisance) would like to safely frolic in the streets. Suburban residents (whose lives depend on fast travel by car) would like to continue affording decent homes.

This competition will appear in city-level politics in various ways. The anti-car side is handing the pro-car side some ammunition when talking about them as subhuman (i.e. framing drivers and people and mutually exclusive categories).