Their argument is not that removing roads doesn't reduce quality of life – their argument is that cities _adapt_ and that tearing away infrastructure for cars in favor of housing and "human-scale" neighborhoods won't necessarily result in doom and gloom.
Of course removing a highway will result in some temporary issues. But cities are living organisms and they can adapt. America is after all a free-market economy. If a road trip to a faraway store becomes inconvenient, a new store will open in due time. If it becomes impractical to drive around, neighborhoods will reconfigure to serve customers within walking distance. And if a hypothetical highway closing permanently were to cause single-car commutes to become impractical, companies will respond by moving offices, encouraging telework, and subsidizing public transit commutes.
We all think we need our cars, but somehow the majority of commuters in cities outside the United States manages to commute via public transit just fine.