I'd better retract my post from yesterday then, as most people seem to think it's fine. I had two issues with it, apart from the stealing electricity point brought up already: 1) leaving a phone with a trailing wire attached lying in an aisle where people would not be expecting it is a trip hazard & 2) in a theatre as old as Her Majesty's goodness knows what state wiring could be in so it might potentially cause a fire risk. Sorry if I sound like a health & safety lecture.
No, I agree with you. Wouldn't dream of charging my phone in a theatre! Though if it's now acceptable maybe I'll bring a toaster next time I go to the theatre, and make myself an interval snack.