They sing and clap because they're happy and they're having a good time. Thats just a cultural difference - people from different places behave differently. I went to a World Cup Soccer event in Foxboro, MA and witnessed that sort of behavior. There's nothing wrong with that - I actually find it almost refreshing - its just different.
These Brazillian tour groups are nothing new - I remember seeing them in the parks in the 80's. I don't remember the sort of rude behavior I see described here, but that doesn't mean it didn't happen. But I guess my point is that they've always been there and they always will be. If you let anybody else spoil your vacation, well thats as much your fault as it is theirs. Try not to take everything so seriously.