Sure, there is an ongoing and very real debate about the effects of gentrification in San Francisco and it's effects - rising rents, change of character, class divisions, etc. The Twitter skybridge is basically a metaphor for how the tech elite believe that they can be literally elevated above the riff-raff of the mid-Market area and stay even more out of touch with the reality of the homeless population down below. Techies can stay high up in their "ivory tower" and avoid having to connect with the normal people down below.