There is a version of the United States where ~60-70% of Americans, including middle-class families, live in urban cores and use public transit in their daily lives. In that world, state and local governments have gobs of revenue and broad political support to fund serious, sustained programs addressing mental health and homelessness. This version depends mostly on building far more family-friendly housing in cities (Everything else flows downstream of that anyway). But it also depends on maintaining transit that is clean, orderly, and safe—enough for example that a parent would feel completely comfortable letting their middle schooler take the train to school.