Yes, before the tech industry, the main source of commuters into the city was the financial industry[1]. My point is that if it were not for the tech boom, SF would be finance and tourism and that economically speaking, the city would be as depressed as Fresno is without the capital provided by tech. Blue collar jobs were moving out --the bedding industry, furniture, etc. had begun moving out a long time ago. Basically people want the economic vitality progress without the gentrifiers --but that's not how it works. Yes, some people will lose out --but overall, you have a stronger more economically stable workforce. Now, in SF we have a problem where even with a good job you can hardly afford new rents. But that's not an issue created by the tech industry, it's an issue borne from bad city planning and NIMBYs --oh, oh, don't build in front of my building, I'll lose sight of the bridge when it's not fogged over. What, no, I don't want shadows from high rises cast over my park[2].
My overarching point is that without tech, the Bay Area would not be the place people come to find good paying jobs --it would be more of a retirement destination and a tourist destination. Let's look at North Dakota, yes, there are homeless despite the boom, but if it were not the for the boom, the state would be in the dull-drums but with shale, whatever you think of it, you have a vibrant economy which attracts all people looking for a way to make a decent living -not everyone will be lucky. That's not to say we should not try to provide for those not lucky (I think we should), but to say that industry creates the "luckless" to me, is disingenuous.
Look at the population trends for SF as a proxy for economic vitality in the 70's and 80's:
1970 715,674 −3.3%
1980 678,974 −5.1%
1990 723,959 +6.6%
2000 776,733 +7.3%
2010 805,235 +3.7%
2013 837,442 +4.0%
People were moving out --there was no new work to be had in the city.
[1]When white collar was basically finance, people used to commute _into_ the city. Whereas now, SF is a place people have a desire to live --it was not always that way.
[2]http://sfist.com/2013/07/18/enemies_of_the_tall_four_seasons...