Many people with kids do what you describe in cities. It's far better for everyone, and even if it's not the superior choice for an individual (though I'd contend it is when you adjust your lifestyle), it is the superior choice for everyone together as it avoids pollution, traffic gridlock and huge fuel inefficiencies.

As it is those with cars push off these negative externalities onto those who choose not to have them, or can't afford them. So your comfort does have a cost, which you don't pay directly.