I think you people are overreacting a bit. It depends of the type of concert you attend. Of course in a musical it's bad to sing along but in a pop-rock concert?
I've been in different type of concerts like Ayu or Lady Gaga and in most of them people are singing. It's not like you are screaming in someone's ear but hearing 15,000 people sing Bad Romance is totally a experience.
I was at Ayu's Osaka show last summer and I sang almost the whole concert, and it was totally fine, and my boyfriend even danced and sang with the japanese girl who was in front of us. But the girl next to me (japanese too) was screaming "Midori" everytime Midori showed up. She was annoying, not me.
People can be bothered everywhere. Not necessarily for being japanese. Just have fun. Anyway when you are there, you read the atmosphere and figure out what you can and can't do
