This is the point. If only activists and journalists are hiding, it becomes very easy to target them. Everybody should care about privacy to protect them and the democracy with that. It's the same as with the free speech. You need it even if you don't have anything to say.

The issue isn't that your history/thoughts are harmless. The problem is that you might consider them harmless, but some authority in the future might decide that you're not one of the "good" citizens.

There are prior examples of this happening in history, eg. there was no reason to believe that your candid answering of a census question about religion in late 19th-century/early 20th-century Germany would ever lead to a young startup called International Business Machines helping your government hunt you down a few years later.