I believe that what I described above is actually the way that private data is defined today: for each sufficiently large data set, there exists a K such that K

I believe that what I described above is actually the way that private data is defined today: for each sufficiently large data set, there exists a K such that K-anonymity means the data is public. If you find it concerning that it's possible to predict behavior based on demographics, I don't know what to tell you. Do you think that psychology studies are an invasion of privacy?