It's not the purchase itself that makes the bank angry, it's purchasing which fulfills the spend requirement and then the cancelling and refunding of that later, therefore retroactively not fulfilling the spend requirement!

Some banks will go so far as to "claw back" the bonus miles they gave to the airline in such cases. But I don't know whether Amex does that.

Many people recommend that if you have to do that, charge (after the bonus posts) enough new charges to offset the refund you're going to get by cancelling the refundable plane ticket (so the bank never has to refund you any money, you just get a credit against further charges on an upcoming statement). It then doesn't seem like you were trying to trick the bank into giving you the bonus (the way it would if you later cancel and never "make it up").

But if all you do is sign up for a card, buy a refundable ticket, get the bonus because of that, cancel the ticket, have the ticket charge refunded, and end getting the bonus with net $0 spend (when there was a $2000 or whatever spend requirement), and never use the card again, you don't think the bank will be angry???