It occurred to me today to compare these three situations:
1. The government cannot require Americans to buy health insurance (so saith two federal judges out of four, so far) because the government is not extending any privilege in return.
2. The government can require people who want to enjoy the privilege of driving on the public streets to obtain and pay for a government-issued driver's license, because it is a privilege and not a right to drive a car on a public street.
3. The government requires people who want to fly on a commercial airplane to obtain and pay for a government-issued driver's license, passport, or identity card, and can prevent commercial airlines from offering their services to people who don't pay for a government-issued identification card, even though the right to travel, in the abstract, is a right and not a privilege.
I haven't drawn a conclusion -- yet.