You want to bring an airline to its knees? Stop accumulating miles via credit card.

• Hold the cards if you want. Pay the annual fee and get free bags, get your companion cert, even put your airline spend on it. But otherwise, put it in the sock drawer.
• Most people would be objectively better off putting non-bonused spend on zero-annual-fee 2% cash back cards instead of earning 1 mile/$1. (Those of you who can continue to eke out > $0.02/mile in value from premium cabin saver awards and the like, I'm not saying stop doing what you're doing, but you're a small exception to an otherwise very broad rule.) Airlines like Delta have worked aggressively to eliminate sweet spots, and most people would come out ahead just taking the cash back and booking on any airline without restrictions.
• It's already well-established that loyalty programs are where airlines generate most of their profits these days, and that flying planes is either unprofitable or marginally profitable. Destroying their mileage sales to partners sends the loudest message you can possibly send.

This applies twice as strongly to people who aren't elite, because then the MQD waivers/credit being dangled as incentives to put spend on a card with otherwise terrible returns are truly meaningless.