Kill the competition
So let's suppose that FB accept this guy's recommendations. That they do manage to harness all the lies, wishes, flights of fantasy and misconceptions that FB-ers put in their profiles (and possibly their posts, too). What then?
They become the most success advertising platform the world has ever seen. The accuracy of their targetting produces stupendous results and advertiers eschew all other media in favour of FB. So all the world's advertising money stops flowing to newspapers, TV and magazines and they all go out of business.
Net result: one advertising monster, serving trivia to the world and bugger all print media, serious reporting, analysis, whistle-blowing or reigning-in (though if it kills off the Daily Mail all that might be a price worth paying). However, most of the quality TV that we import (let's forget about ITV and other commercial UK TV as lost causes and not worth their bandwidth) into the UK would be gone,too.
So maybe FB already know how to leverage advertising. Maybe their analysts have performed an in-depth analysis of the consequences and decided that while they could do that, it wouldn't serve their purpose (as they'd also kill off most commercial websites and ad-dependent searches, thereby destroying the attraction of the internet which they rely on) and therefore they choose not to dominate - primarily for their own benefit.
Sometimes you have to let the goose have it's freedom to continue laying those golden eggs.