Yes, the hoarded data is per se dangerous. It should not exist, as in, it should be very illegal to collect and retain. That goes for non-tech companies that do similar things, like credit card companies.

[EDIT] That is, things like credit card companies selling your purchase history. Obviously they do need to retain some of that information to operate, but they shouldn't be able to sell access to it or use it for any other purpose. Ditto banks, magazines selling subscriber lists, all that crap. Should not be legal.