They can't see how much I paid for a car when I paid with a cheque either. This is not a problem that I, or 99% of human beings have.

Again - what is the darknet supposed to protect me from?

Seriously, I have yet to hear a single legal use case that Bitcoin improves.

Transferring large amounts of money overseas for large purchases is cheaper, faster and safer than using the current banking system. So that's at least one legal use case Bitcoin has improved for me. Even after exchange fees and miners fees, I paid less in fees then I would have using a bank and the transaction confirmed in under an hour vs several days or more through banks.

Mainly referring to the credit card companies that will sell your data.

1. You don't buy a car on a credit card. Dealerships won't even accept cards. Private individuals won't, either.

2. Your counterparty (the dealership) will sell your data, regardless of whether you pay with cheque, cash, bitcoin, gold coins, or lost pirate treasure.