"It fundamentally changes the relationship between people and state." is the most ironclad argument I've heard. Albeit a bit of a cliché these days.

There's some advantage to the tin foil hat, too. It's probably fine for now if you're not Muslim, but if you are then your associations and visited websites could be used to put you somewhere very uncomfortable without a trial. Say if libertarians or socialists or christian conservatives started carrying out attacks, your political and personal affiliations could make life very uncomfortable.