I completely agree about the feedback loops. They're mutual feedback loops though, and causality can go both ways. We're currently stuck with a strong attractor of surveillance-based software. It's certainly possible to escape from the local minimum, but requires a lot of activation energy to escape it (compelling functionality, features, ease of use, etc, to prime its own network effects).
I don't think it was ads per se, but rather the centralizing software architecture of AJAX (et al). Everyone wanted to build things that were "easy" for "everyone" to use, how to make money came later. Or going back even earlier, if "the web" had been designed around something like content centric networking rather than HTTP.
On "tech moment right now is ripe for it" - for me, it has felt this way for the past twenty five years! I generally agree about pessimism as well, so let's just say at this point I'm tired. I certainly don't want to dissuade you from pouring new energy into software that is going to change the world [for the better]. But I'm also cautioning you to not reject other angles of reform!
Further on the pessimism point, isn't shying away from government (ie collective) action itself a form of pessimism? I'm pretty pessimistic about groups (herds) of people in general (things always end up going "sideways" due to opportunists). But looking at the structure of US politics it seems there is a large contingent of "government can never work" that ends up running interference whenever de jure government tries to reign in the corpos (which tend to act as de facto government), creating a self-fulfilling prophecy.
Or putting my general point another way, in terms of the culture point you made elsewhere - our mass culture is currently strongly steeped in centralized political action/narratives. If you want our mass culture to change to value technical decentralization and privacy, then one of the main things you'd expect to manifest itself is a call for centralized/government action, ala privacy regulation, right? We can certainly lament the centralized political culture, but unless you're talking about changing two aspects of our culture simultaneously, then that basically is what it is.