You should stay the fuck away from concerts, then! Man... Part of the fun for many - including the band - are the sing alongs.
Listen, man.... I know what you're saying, and it seems to make sense as an
idea. When you're talking about an arena, then it works. There are enough people that the pitch discrepancies read as a chorus effect, and it sounds huge and awesome. It also works if everyone plays along.
The problem is with seeing the band in a club or other small venue, and mere pockets of people, possibly drunk, lacking in talent, voices strained to be heard over the PA's, decide to sing along.
Especially when that pocket is right next to you. And
ESPECIALLY, when it's not in a "sing along" part. You have to read the situation. I was at an Opeth show and we all sang along to the chorus of "In My Time of Need", and it was a cool experience.
Bad experience: being at a Tori Amos show, and during her acoustic set, the fairy winged teeny boppers in front of me decided to sing along to every song, regardless of whether or not they actually knew the lyrics or the melody. It was painful, and I had to resist the urge to throttle them. They had the fucking nerve to say, "Isn't Tori great?" between songs. As if they could even hear what she was doing.
Great experience 1: Iron Maiden - The Trooper. Singing along to the "Oh oh oh oh oh oh oh oh oh" part. Cuz you're SUPPOSED to. (See also, Fear of the Dark)
Great experience 2: Not very metal, but it was a Ben Folds concert, and, without Ben's help, the crowd spontaneously sings the missing harmony lines and even horn parts. A VERY musically talented crowd. Blew me away. There's some stuff like it on his live album, but they were coached. Our crowd wasn't. Totally sweet, and a memorable, fun experience.