In most cases no-one will want to blackmail you. But people do blackmail journalists, judges and/or political figures with power. There is a track record of this sort of thing having been done even in countries like Canada (where the wife of a former PM was illegally monitored to try and get dirt on the guy). Or look at Nixon and Hoover.

In any environment where mass surveillance is technically possible and hidden from effective and comprehensive public oversight, abuse becomes permitted and hidden.

So standing up for privacy is not just a matter of protecting your own identity (although that is frankly reason enough). It is about protecting the conditions under which a free press and democratic society can survive, and in which individuals can act according to their moral conscience even when such conscience leads them to oppose entrenched power structures. And you should care about what happens in the United States not only because God knows how its security apparatus will use this data against your own country and elected leaders, but because American discourse influences global perceptions of what is seen as an acceptable level of state surveillance in other countries.