Regarding live sound at metal shows

Well, we certainly don't need metal bands to be quiet. Non-metal concerts aren't quiet by any means, they just aren't so loud that the sound gets muddied and people's ears don't ring after the show.

Keep it around 90-100 decibels and I think everyone would be quite happy.
 
It usually has to do with the bass to me and not the volume. It seems a lot of places/bands just crank it all the way up causing the rest of the sound to get muddied. I went to a show at the Webster in NYC a few years ago and the bands themselves were fine (was a rock show) but the in between music actually hurt the bass was turned up so much. My friends and I were joking that they had found the brown noise.
 
In most clubs the stage is way too small and the audience can get too close to it. The best spot soundwise is always where the mixing table is located, whic usually is the acoustic center far from and straight in front of the stage. Standing too close between the speakers or far on either sides will have the effect like hearing mono sound or only one channel in stereo.

This is why most people who complain about the PPUSA sound need to either move back by the board, or get off their lazy butts out of the seats and come down by the board before saying the sound sucks. I forget the guy's name that does most of the PPUSA sound, but he does a great job of keeping the overall sound decent and not too loud. It's only when the headliners bring in their sound guys (like Angra a couple years back) does things get crazy loud IMO.