The industry accepted threshold for instantaneous hearing damage is 140dB. A 6ARC shot out of 18" rifle with a decent suppressor will produce somewhere on the order of 128-132dB at the shooter's ear.
After nearly 60 years of experience I make no judgments on suppressor use. Smoke'em if you got'em.
There are Pros, Cons and Compromises.
Facts are facts, from a military perspective they are a necessity. Shooting supersonic ammunition suppressed without hearing protection can damage your hearing.
You can shoot subsonic ammunition in a firearm where the action needs to be cycled manually where the only sound you hear is the striker drop, the bullet hit and a very, very, very, soft pop. If you're indoors in a confined space with the windows closed you will feel a pressure in your ears and smell the powder burn and possibly the fluid in a liquid suppressor. There is (if memory serves) a very effective Russian suppressed revolver.
There is a hearing disorder Meniere's and I've seen suffers of this have dizziness and balance issues with repeated firing suppressed indoors, in closed environments. Between the effect of the change in airpressure to their ears and the smell of the propellant it can be a not so pleasant experience. I find it smelly but rather quiet to shoot.
You can shoot subsonic ammunition in a self loading firearm that will cycle the action and in addition to the above sounds you'll hear the action cycle and the brass fall or possibly go into a catcher. The sound of the action cycling is loud.
A suppressor is a very useful tool, but requires reasearch because while it's useful when used properly, it can be dangerous when used carelessly. I do not currently have any suppressors.
I use ear plugs under my ear muffs at the range, I use hearing protection in the field. I use a muzzle brake on my self loading rifles with intermediate cartridges. I practice drills hitting steel at 300+ yards, the drill is to launch round 2 before round 1 hits.
My heavy rifles have no muzzle brakes but use recoil reduction techniques, weight, recoil pads and balance.