Although the airlines certainly benefit from the ID requirement, I disagree that airline revenue protection is the sole purpose of the ID requirement.

After 9/11, it was determined that only ticketed passengers should be allowed past the security checkpoint, for two reasons:
1) Reducing the number of people in the sterile area theoretically reduced the odds of Bad Actors getting through to a plane
2) Reducing the number of people being screened at security checkpoints eased the burden on the newly-created TSA, which shortened long security lines and allowed them to focus only on people who were actually getting on a plane

However, after that restriction was put into place, a number of incidents throughout the 2000s showed that it was ridiculously easy to pick up a discarded boarding pass and gain entry to the sterile area using someone else's ticket. In fact, one person was apprehended with numerous BPs in his backpack, most from flights that had already departed, many from previous days - they got him into the sterile area, because TSA was lax in checking the dates and times on the BP to determine its validity. The BPs were also in other peoples' names, leading to the question, "How can TSA know whether that's really YOUR boarding pass?" And so, the requirement to show ID that matches the BP was born, not for revenue protection, but out of a vague, undefined sense of fear that someone traveling under an assumed name is "up to no good" and poses some sort of threat to aviation security. Coupled with the outlandish notion that showing ID somehow roots out terrorists and criminals (as if they all have the word Terrorist stamped on their IDs or something), this convinced the general public that ID requirements were a genuine security measure.

The holes in the logical arguments are clear, starting with the fact that it's so easy to obtain falsified documents and use them to obtain genuine IDs under false names, and leading up to the realization that even if you travel under an assumed name with false ID, you still have to undergo exactly the same security screening as everybody else, making the ID requirement absolutely useless anyway.

The airlines never protested the ID requirements, because they do derive a benefit from it. But they're not the drivers behind it, and don't deserve the blame. The blame rests in two places - the flim-flam men at TSA who constantly repeat the false mantra that "ID Matters!", and the general public, for being gullible and paranoid enough to actually buy the lie. But I'm not going to lay this one at the feet of the airlines.