"The first principle is that you must not fool yourself and you are the easiest person to fool." - Richard Feynman "You Yanks don't consult the wisdom of democracy; you enable mobs." - Australian planner
Recent studies cite housing costs as a primary driver of homelessnes, not mental illness and addiction, but those remain components.
Here's Charles Mann's short version of his book 1491 delivered as a lecture. Highly recommended.