The volume you are exposed to depends on how close to the speakers you are. In a large venue the people closest are getting a lot more sound than the people in the back
And yet, I've been to plenty of venues that were uncomfortably loud in back while not going to any (indoors, professionally set-up) venues that were uncomfortably quiet in back.
I think it's more than what you've described. I think it's that a lot of folks actually prefer dangerously loud volumes, and this contributes to a positive feedback loop of expectations for loud concerts. I wish most concerts were quieter, but I may be in a minority.
What you're saying sounds great in theory but unfortunately it often isn't the case. I've been in small(er) rooms in clubs where the sound was still "blow your eardrums out" even in the back.
Anyway, the solution for "it's quiet at the back" isn't "turn it up at the front". It's line arrays, distributed speakers etc.
Safe is a matter of intensity and exposure time. There can be a volume thats ok for occasional exposure, and desirable to the audience, but not safe for repeat exposure by musicians. I wear earplugs when I play in a "quiet" jazz band. I don't wear them in the audience at the symphony.
