&gt; When you newly learn that a person is a part of ISIS (for example) you can look through their entire communication stream retroactively.<p>The problem is the same can be applied to {{political_opinion}} such as $has_been_to_rally(tea_party) or $is_member(nra) or $has_donated_to(aclu). Then, tptb can glean through all the past records of anyone who is starting to gain momentum (and trust me we all have broken laws one way or another if we look finely enough).<p>My argument against a surveillance state is not based on whether it can stop acts of violence but rather my question is &quot;at what cost?&quot;