Sure, there have been nadirs before, the 80's after all industry left and only some financial services were left downtown --there were vagrants and muggings but for the most part, if you kept away from the bad neighborhoods, you were unaffected.When I first came to SF the city was int he grip of a crack epidemic and. I've seen people get shot in the face broad daylight and been in the middle of a driveby. The city is going through an uptick in crime at the moment but its mainly property crime. I don't feel significantly less safe, though that's partly because I have a lot of experience with unsafe situations.
A large part of this is simply driven by poverty and prices. Policymakers, business owners, and pundits naturally want a city full of high-earning go-getters whose money will increase the general level of prosperity, fair enough. But there's some sort of naive belief that people at the bottom end of the scale magically teleport themselves away to other labor/residential markets where they'll be more competitive, because economics class made it look just that simple.