I'm convinced Zuckerberg's infamous "dumb fucks" comment was made in a state of puzzlement that all these n00bs just had no idea they shouldn't be giving him that info, and indeed, the dawn of Facebook and all the people it added to the set of folks posting information online ended the previous "no-one knows you're a dog" set of norms of the Web.
Now there's money tied up in it, so of course people insist they must be able to post all kinds of things under their real names so they can market themselves. Never mind that it remains a terrible idea.
This is the source of conflict, I think, between people who want more real names online and those who want none. The former are the new folks who think posting personal info online is normal, or even necessary (see again: personal brand-building and marketing) and believe that we need to be able to ID everyone to prevent abuse (i.e. be able to find abusers to punish them), and the latter are the old-school Web users (post-Eternal-September, pre-Facebook) who don't get why all these idiots are making themselves easy to abuse in the first place, who see more anonymity as the obvious cure.
I think there is a space for both, tbh. There is always business based on reputation, and for that you need to self-identify. I used to be a professional gigging musician, and there was absolutely no way to do that while remaining anonymous online, nor would I want to.
The difference being, I suppose, was business vs personal, but personal brand was a thing long before the internet (I assume).
You also have to keep in mind that you can be publicly divulging things without even realizing it, especially because everything you post online is stored permanently, and tons of private information about you can be extrapolated from it by anyone who bothers to pay attention.
It's also insanely profitable, just look at Google and Facebook!
For Facebook, they make money from advertising to logged in users. Broadly speaking, they keep users logging in by offering users the ability to broadcast private information to friends, and by offering the ability to receive such broadcasts from friends. To the extent FB does invade privacy, they do so to more effectively advertise to users on their site. They don't make the results of that invasion -- the profiles they build from their tracking bits, in other words -- available for public search. What's available for public search is instead only what the users choose to broadcast about themselves.
The exposure of private information to public search engines is not what is profitable about either of these companies. It's an incidental effect of the persistence of digital storage and the difficulty of curating what is stored.