The counterargument . . .
. . . is that it doesn't *have* to be that way. Back in the Internet's salad days, there were sufficiently few people using it that, if you talked to enough people, you could probably track down the real identity of an individual, but no one (except possibly the FBI) was explicitly gathering personal information. If you were an asshole in a moderated forum, you got banned, but you could easily come back with an alt. Facebook and Google are now working hard to tie your Internet identity to your real identity AND scarf up a mess of data about you. Exactly how bad that is depends on your perspective and what you personally get up to, but I don't think anyone would disagree that giant databases of information which can be used to tie up vast amounts of personal data which can then be used to identify the proclivities of specific individuals and/or commit crimes of data, identity, and financial theft and fraud constitute a tremendous risk to the people whose information in those databases.
The typical El Reg reader seems to be of the perspective that people who use Facebook or other social media (or indeed the Interwebs at all without 7 proxies and a pseudonym) get whatever they deserve. This perspective fails to acknowledge that most people are not aware of these issues to the same extend that most Reg commentards are and further does not address the fact that at least a subset of this information can be scarfed in by illicit/clueless Web programmers.
I personally try not to put anything on the Internet that I wouldn't want my mother to see, but not everyone is so careful. In any case, when one shares information with one's friends, one probably doesn't expect to see that information spewed out for the world to see, regardless of the content.