Old-fashioned pre-amplification buildings with decent to good acoustics tend to sound worse with reinforcement. And if you have a nice quiet audience, it's lovely. But a place like a gymnasium? It's practically a must if you want to be heard at all.

I don't think it's just modern noise pollution -- although I suspect we do suffer much more hearing damage than in quieter centuries.

In addition to the physical spaces, I think audiences and musicians behave differently. Audiences are louder and musicians (particularly singers) have less training in controlling the volume of their instrument. And events are usually about filling the room with music instead of allowing the back to be nice and quiet where one can carry on a conversation, while those up front enjoy the music.

Sound reinforement has definately changed the dynamic between performer and audience. Successful acoustic events seem to require the willingness of both the audience and the performers to make them happen. Whereas with reinforcement, one can be heard with or without the permission of the audience.