How many complaints do we make as controllers that the general public knows bugger all about air traffic control.
Then we go and make it difficult or impossible for them to visit a unit to maybe find out a bit more. I don't agree with the "unless he is a controller or aircrew".
If the right security checks are in place..I see no problem with visitors outside of the aviation sphere. It might start to break down some of the barriers between us and the flying public that so many people in here seem to despair of!