The web is a big place, much like the rest of human culture, and there's no clear evidence that it can't both be a dance hall for most and a library for others. Culture has had that problem for millenia, and we have developed numerous mechanisms for coping with it. There have been countless books written over the centuries, and even more lately, so how come I can consistently find sources of the best literature written by man? The same mechanism, curation and word of mouth in circles that care about quality, will apply in the future, as it did in the past.
Your retort to this might be, "but most people don't have access to this curated content supply, they're stuck with the manipulative garbage produced for the masses". But that's always been the case, and it's not specifically an internet problem. Different people have different value-needs. Not everyone wants to read Dickens. Some people really just want to read Mills&Boons. The same is true on the web.