This is a contentious issue and in case you are not from SF and wondering why Y Combinator is taking a stand on it, it has to do with the politics of the tech boom. The plain truth is that the housing crisis is a combination of too much sudden demand fueled by the tech boom and too little supply. The tech community likes to deflect criticism of their sudden influx of relatively high-income workers and say "don't blam…
"The problem is that the building and real-estate industries have a huge lock on California politics."
San Francisco is the #1 most development-hostile major city in the world. According to World Bank data, even in places like Ethiopia and Zimbabwe, it's still much easier to get planning permits than it is in SF. Blaming the power of the real estate industry for San Francisco's rents is like blaming the Chinese famines on capitalist saboteurs.