Which is the only real alternative. This is not such a radical idea, really. The mortgage money goes to repay the city's investment in construction. Your home becomes a place where you live, not something you invest in to make money. There is no speculation.
Prices are stable.
The city gives first preference for this housing to longtime residents of the city who are being evicted. Young, single people who have just hit town go to the end of the line. Senior citizens who have lived here their entire lives and working-class families who have been a part of the community for a long time, get to take advantage of the opportunity to stay here. If the city had seized the Mission Bay land by eminent domain in 1985, when it had the chance, there'd be room for maybe 20,000 of these new units in that area alone. But the model isn't limited to new construction.