Binary classifiers used to determine your political allegation and/or support of some terrorist organization based on your tweets. What could possibly go wrong?
That is a good question, and one we should discuss more actively, because if it can go wrong it will go wrong. What happens when an over eager politician learns that "we can predict with X% accuracy if a person will do something bad next year"? I might be cynical, but I do not expect the result will be an increased interest in how society can help people before they do bad stuff. It would not surprise me if instead the argument would be that extensive surveillance is a great benefit to society because it can identify the bad guys with X% accuracy.