Of course it is horses for courses. In the past I had the chance to go and see the Beatles. The tickets were expensive and in the end I decided not to go as I knew I wouldnt actually get to hear much with people screaming etc. So stayed at home and a friend who actually went , said you couldnt hear a single song for the raquet but that the atmosphere was great etc. But the expectations for a pop concert are very different to other things.
I am a classical singer and have also been in opera etc. After all the effort and work to become word and music perfect for something, I would be rather miffed if it was all spoiled by someone singing aloud and spoiling all the dynamics etc. and of course they may also not be in tune. Some things seem to lend themselves to a certain amount of joining in chorus and I find especially the chorus in G@S as the audience are usually devotees who just about know every word. But when it comes to other classical things, I dont like people joining in. Partly when you have a chorus singing or perhaps a duet or trio by the singers, a lot of the pleasure is hearing how the melodies of the different singers intertwine with the other singers making a lovely pattern to the song, which is what the composer wants you to hear. So I recommend people remember them and enjoy singing them on the way home!!