Problem that I have with PA is that it kills the chorus. I love to sing anything with a rabble rousing chorus and I can almost always get the whole crowd to belt out "midnight special" or "16 Ton" (folk???)
Do the same thing with a PA and the participation drops way down.
I went to the beer tent at a recent festival and the performer (amplified) was moaning cos nobody was joining the chorus...well I couldn't even hear if I was singing in tune unless I put my hand on the side of my head (very folkie that!) so I gave up too.
I think that amplification creates a performer/audience divide and the audience goes back to passive/apathetic mode.
I've been to many a festival where the power went off temporarily and the audience and performer were having a great time for several numbers, then the power came back on and it was back to normal and not half as enjoyable.