Well actually there is some merit to the concept of it. Hearing loss and protection has been something that I've been personally interested in. For those who may not know, UM's not really my primary focus in life, and I'm actually currently a medical student and work in a research lab that targets the mechanism of hearing loss as part of the school curriculum. I'd love to share my thoughts on this issue through my, admittedly limited, medical background while keeping any bias as an MOT out of the picture. Of course, I know that's not totally possible for everyone in the community to accept, so feel free to take this with a grain of salt.
So first and foremost, yes listening to music at 140 dB causes hearing loss, and is the primary cause of hearing loss. There's no argument to be made there. Individuals, especially of my generation, are probably the biggest offenders and contributors to hearing loss by blasting their ear drums to oblivion. But it's also important to note the mechanism in which that occurs and how acoustic pressure differs from air pressure.
I'm sure many people are familiar with this already, but breaking it down to the basics, your awareness of your surroundings can be broken down into two part - sensation and perception. Sensation is your physical connection to the world, like touching a hot stove, and perception is how your brain interprets that signal as something that's going to hurt your hand. When you're listening to music at dangerously high volumes, you're not only risking damaging the stereocilia in your cochlea, but you risk affecting the sensitivity of the action potentials of those cells. When you drink coffee, your body desensitizes and learns to deal with it. Similar story with loud listening noises, except that the effects are more permanent.
On the topic of pneumatic pressure, I'd like to start by saying that I'm not the biggest fan of using that term in this scenario. The term is technically correct, but I feel is really more associated with mechanical engineering and such. It makes everything sound a bit too scary. Anyways, air pressure can damage the mechanism in which you sense the sound signal itself. That's called ear barotrauma. It also sounds a bit scarier than it really is, as it's otherwise known as airplane ear and is something that is, well, not serious at all. Your body's able to normalize the pressure between your middle ear and canal by opening the pharyngotympanic tube, AKA when you yawn or swallow. Continuous exposure to air pressure can lead to hearing impairment, but even then, the effects are generally reversible and not a big issue. So why bother bringing this up then? Because chronic ear barotrauma can be linked with permanent hearing damage and in rare cases may need to be fixed surgically. When you're plugging and unplugging your IEMs in and out multiple times a day, you're exposing your ears to changes in pressure. Not to mention the fact that basic facial movements change the shape of your canal, and the pressure of your ear canal as a result. Imagine a vocalist (or someone who enjoys singing along) singing for 2 or 3 hours straight exposing themselves to that constant change in air pressure. Rinse and repeat, and those things can add up. If you have a custom or a deeper inserting IEM, you could find that the tonality of the IEM changes when you raise your eyebrows or when you open your mouth, or that the sound is straight up at a lower volume. That's due to the change in pressure in your ear canal physically impeding the tympanic membrane's ability to sense the signal.
Just some food for thought and maybe some info that people may find helpful or interesting. I certainly don't blame individuals who view it with skepticism, but, again, I do think there's merit to the concept and that the science is sound (ha.... get it?...).
Although I did have a lot of fun along the way. 
) - but those are just my two cents.
