Its always been expensive to live here, it doesn't have much to do with tech, it has more to do with SF being a center for finance AND technology. That said, having a mortgage lower than your rent is true for many people who bought at "the right time" rather than at the peak of demand. Demand is outstripping supply due to the insane people who get elected to the city government, which is largely driven by fresh but naive stream of tech workers and the radicalized longterm residents. The only way to fix this is to oust people who do not support fiscal security and personal freedoms (Leeland Yee is at the top of my list) and replace them with people who eschew cronyism and support a balanced approach (Sean Elsbernd comes to mind).
The so called BART divide is really more about greed and institutionalized mediocracy. Station agents should make minimum wage, the people who make BART actually run are the maintenance staff and the conductors. The conductors shouldn't be people in trains, they should be people in offices as the technology for having fully automated trains has existed for decades. The safety issue is a red herring, as the issue as posed is not for more transit police, but for more lighting. Management is also not blameless as they should be putting less money towards bureaucratic salaries and returning it to the ridership in the form of lower fares and upgrades to cars.
If you feel guilt about living and working in SF, stop it. Spending money is what keeps the economy of SF moving, and what keeps people who don't work in the tech industry employed.