When people sing with the artists performing, it gives the artist a sense of comfort. It's easier to hit notes in my personal opinion. If the crowd didn't sing with him, we might hear more flat or sharp notes than we would if the crowd wasn't singing with him. Plus, an eerie, silent crowd is pretty nerve wracking. :P
@cybertron39 I saw him live he says he loves it when fans sing with him because it makes it so real. if you watch other live concerts you'll see he asks people to sing with him
