henry, you're opening a bag of worms there. Drums are naturally loud, and each muso wants to hear their instrument a little louder than they can hear the rest of the band, so they can 'lock in'. Thus, everyone continues to turn up.
Music also naturally sounds better loud, and to get a good even mix, it's a matter of having the PA louder than the sound coming off stage.
Generally punters should be able to endure 2 hours without hearing damage, but ringing ears while they go to bed happens.
Concerts do sound better with earplugs in, especially if they're properly designed earplugs for even frequency response. The reason it sounds better with them in is because it helps reduce the sound of reflections of soundwaves bouncing of walls, seats, etc so you're hearing the direct sound, without any reverberation.
A lot of technical advancements have occured in the past few years to getting even frequency response and coverage out of concert PA systems, which slightly reduces the possiblility of hearing damage by perhaps not being blasted with painful frequencies such as 2khz depending on where you're standing, however efficiency of speakers and amplifiers have also improved, increasing SPL:distance ratios.