I think that there's a level that's "just right" for any particular type of music in any venue.
If you're in a pub, such as my local which isn't a specific music venue, a rock band should be loud enough that you can feel the bass a bit - not so much that it actually parts your hair and physically removes your kidneys - but rock has to be felt a bit in order to be rockin, same with funk.
However, a chap doing folky stuff with an acoustic guitar shouldn't be anywhere near as loud as that (although in my book he/she wouldn't be allowed in in the first place )
And neither should be so loud that you can't easily order a pint.
An whatever happens, the sound should be clean - I don't mean no distortion effects obviously, just that the PA should have sufficient headroom not to clip every time a note is played.