The "terrorists" argument always seems like a big red herring in these discussions. But it's an interesting point that if the government decides you are a "terrorist", which maybe they can do without you ever being convicted of anything, you can be shut out of much of society by being deprived of I.D.

On the other hand, somebody the government doesn't suspect can simply sign up for I.D. like anybody else and carry out an attack at their convenience.