The question of concert behaviour, like most codes of conduct, depends on where you are. Who are you upsetting by ignoring etiquette? Does that etiquette have any purpose beyond crusty tradition? As far as classical music is concerned, the answer is yes. The need to sit still and pipe down is purely practical: to enable everyone to hear properly and to respect the performers, as well as fellow listeners. No one cares what you wear any more, and all that social nicety stuff is dead.
The London Philharmonic Orchestra's Vladimir Jurowski addressed this question after conducting Beethoven at a free-spirited beer-and-crisps concert at London's Roundhouse. While he could tolerate chatting and tweeting at this non-classical venue, he conceded that at the Royal Festival Hall any unnecessary noise is a distraction. Who, of a classical tendency, hasn't sat next to someone whose noisy breathing – yes, that's how much we mind – has prompted murderous feelings? Chewing gum fixes itself in your line of vision and the jaw action is never in tempo with the music. Fanning yourself with a programme is actionable. If you are hot in your skimpy sundress, the performers in heavy concert wear are certainly boiling. Rustling plastic bags, jangling bracelets, fiddling slowly and painfully with crackly wrappered cough sweets… don't get me going. In another life I would wear a uniform and police them all.
I am one of Jonathan Harvey's most devoted fans. His music is exquisite and delicate. Because of its experimental nature, it is often amplified, and I suppose it would be possible to hold a low conversation while it's being played, though I can't imagine wanting to. I am wholly sympathetic to his desire for adventurous collaborations to keep music alive and bring in new audiences. There are many ways. Moving around in concerts, unless advertised as a peripatetic exercise, isn't one.
Would football matches be improved for the uninitiated like me if we were encouraged to wander on to the pitch and maybe give the ball a kick? It's an idea, but I doubt it will catch on.