So what? If everyone did it then people would be furious but they'd still have to fly. I doubt folks will start driving ORD-NYC when frequent flyer programs are gone.
This was in reply to the assertion that most people don't care about miles. My point being that while most people don't care, "most people" don't matter here. Regular customers of the airline (not "most people" and not just elites) do most of the travel, bring in most of the revenue, and do care about their miles, frequently making purchasing decisions based on them.
For every one of me who flies UA because of miles there is someone who flies AA because of the miles and DL because of the miles, etc. It's all a wash, AFAIAC. So, why not just get rid of the entire scheme?
An interesting point, and one that should worry frequent flyers. My response to this is that the airlines make serious money selling miles to banks, restaurants etc. which keeps the programs we love profitable and viable. If this revenue stream disappeared, one could use this argument to separate mileage-earning programs from airlines.