“At the Greer Garson theatre, absolutely NO non-performing arts majors are allowed backstage. There’s no other reason, okay, well maybe it’s a slight liability issue too, but the belief it is bad luck to have an audience member or such behind the scenes.”
My actress friend told me this. In my experience, thespians are a pretty superstitious bunch. However, I imagine this practice originated in the practical issue of actors and crew members not wanting to have to deal with extra people getting in the way of heavy moving sets and quick changes.