It might be legally significant, but technically, there is no real difference. Given your social network, and training data consisting of the public members of

It might be legally significant, but technically, there is no real difference. Given your social network, and training data consisting of the public members of a group you can use a semi-supervised learning algorithm to determine group membership. Since social networks have a small diameter and the public members are typically well connected, you would expect this approach to be fairly accurate. Or rather, accurate enough to act on, if you do not need to provide legal justification for your decision. What's the required legal justification for putting someone on a no-fly list? If you want to give some real world basis to the legal distinction you need oversight and transparency. In particular, global analysis of the whole dataset must be illegal, since it pretty much corresponds to total surveillance. Your results might not be completely accurate, but they don't need to be if you can act once you have something like 51% confidence.