They are absolutely right with this. You have hundreds of people taking the same pictures - and for what? One of the best shows I ever went to, Jeff Mangum, had a strict no phones policy. They even escorted a couple of people out for violating that. You should be there to enjoy the music and performance, not to take pictures to add to your Facebook collection. The mosh pit is still alive and well at a lot of smaller shows! === Fun fact: Most contracts for music performers at college concerts include clauses barring them from encouraging mosh pits and other similar acts (if they happen they happen, but you can't incite them). They also bar physical contact between the performer and the crowd during the set (IE no surfing onto the crowd allowed). These rules aren't always enforced, but one more thing to keep in mind. Source: I've booked shows at my college and have had the opportunity to read through a couple of contracts.
That fun fact isn't fun! One of the coolest music moments I've ever seen was [Alex Ebert](www.allmusic.com/artist/alex-ebert-mn0001967279) in all his bare-footed glory walking around on the upraised hands of hundreds of swaying hippies. Physical contact should be up to the performer. And damned if I didn't touch Astronautalis a few weeks ago and damned twice if it wasn't the highlight of my hand's day.
I just realized I omitted a very important word in my comment. Everything in that fun fact pertains to concerts located on campus at colleges.