Unnecessary. OSHA measures sound levels in manufacturing areas, and if they exceed a certain level, the company is required to post warnings, and provide (and enforce the use of) hearing protection. They don't mandate the company "turn the equipment down".
Likewise, I'm all for all concert facilities posting warnings about sound levels, and suggesting the use of hearing protection. If they desire, they can go so far as to sell earplugs to those who want (or forgot) them.
I DO NOT agree that we need to "idiot-proof" the world. The next thing we'll hear is that we need to wrap everything on Earth in Nerf material so that no one gets hurt by touching anything.