I'd like to start a cheap, anonymous medical clinic. We'll screen for blood diseases. We won't check identification, but you're expected to give us contact information: if you test positive for something, we have to let you know. We'll also give your blood back after we're done testing.
Hopefully we can get a lot of people using the clinic. I realize there's a bit of trouble if someone comes in and claims to be you and has Hepatitis B, for example, and you come in and are clean and we inject you with his infected blood, but hey! The important thing is that someone knows that someone had Hepatitis and that infected blood is always returned to someone. We sure don't want to keep it around!
(One of my housemates points out that if the situation were reversed if the Internet were run like the medical industry you'd have to fill out a dozen forms just to send e-mail. I just pointed at the Sendmail book.)