Even if you have nothing to hide, you'll benefit immensely when, e.g., people with something to hide reveal your leaders are trying to goad you into a war under false pretenses.
To say nothing of how much the perspective changes if you live in a place like Russia or China. Historically, times and places where a good, honest person could bare their life to the government were few. How sure are you this period of relative beneficence of our governments towards its citizens will last, that you dare throw away yours and your children's freedom on the bet your future masters won't mean you harm?