Usually these discussions sound like some people are worried that the corporations themselves will do something bad with the data (sell you more stuff you like !gasp!).

Government misusing data is the only thing I could think of. But what's the evidence for that fear? If the organisations you mention wanted to go after people, can't they already do so?

With this kind of reasoning, the internet itself should qualify as a huge setback to privacy. The point is that the advantages far outweigh the disadvantages.