It's ridiculous. Just because your info might sell for $20-40 (or a few hundred dollars, depending on how much you give away), it can cost you tens of thousands of dollars to recover from identity theft. If someone opens credit cards or takes out loans in your name, you will initially be liable for them, and you will have to pay hefty lawyers charges to investigate and resolve them. They can use your details for tax fraud, and land you in serious trouble with the IRS or your nation's equivalent. They can commit insurance fraud, and claim against your insurance policies (including medical). They can even land you with a criminal record.

It can cost huge sums of money and take years to recover from identity theft. You can end up with a useless credit score or a criminal record. It just simply isn't worth it for a $20 airdrop.