there's only so much you can do. That's not really true, per the linked article above.
As far as I'm concerned the lack of cheap housing in San Francisco is no more of a problem than the lack of cheap housing in Beverley Hills.
See Edward Glaeser's Triumph of the City for more about why this is a problem. For example, he cites an array of research that comes to this conclusion:
"Cities enable collaboration, especially the joint production of knowledge that is mankind's most important creation. Ideas flow readily from person to person in the dense corridors of Bangalore and London, and people are willing to put up with high urban prices just to be around talented people, some of whose knowledge will rub off.
Rousseau famously wrote, 'Cities are the abyss of the human species,' but he had things completely backward. Cities enable the collaboration that makes humanity shine most brightly. Because humans learn so much from other humans, we learn more when there are more people around us. Urban density creates a constant flow of new information that comes from observing others' successes and failures" {Glaeser "Triumph"@247}.
In other words, having a large concentration of smart people leads to new ideas and "the joint production of knowledge." Preventing people from moving to cities through price restrictions means less knowledge and has an array of negative environmental consequences.