In biology, the more successful a species is, the more parasites, predators, and pathogens adapt to attack it. This means that over time a species has to change in order to survive, or die off by massive and continued attrition.
Technology, I think, evolves in the same way. It isn't static, it responds to markets, new techniques, and new threats. It can be exploited both technically and socially. And of course, the bigger the target in terms of both users and codebase, the more valuable and vulnerable it becomes.
This is a rough way of saying: I don't believe a world scale system like this could ever marshal enough continuous investment to respond to the enormousness of the capital that will be spent breaking it by criminals, spies, and probably advertisers.
The question of establishing trust in the world has always been hard, even before computers. It is harder now, and the odds are against us.