Different air travelers can pay very different prices for the same seat.

Airlines can't directly tell how much money a customer has, so they find indirect proxies.

Business travelers (reimbursed by their employer and thus not very price-sensitive) have identifiable patterns. They prefer particular flights on particular days of the week, tend to buy tickets close to date of travel, etc. Airlines exploit this to charge them higher prices.

If two consumers purchase the same item at the same time, it should be the same price. That's what we're debating. If an airline raises prices closer to departure, then that's not a violation of privacy, nor discriminatory in the sense we're discussing here.

I do, however, object to firms aggregating any individual's purchases across different interactions. That data should belong solely to the individual and it should be illegal to retain enough information to aggregate interactions across interactions with the same customer.