I did read that part, I still do not see how that justifies closing the museum terrace. The people photographing and sharing online pictures from the flat isn’t on the museum. Make the museum forbid to take pictures from the terrace if that’s the main source of concern. The museum didn’t create the terrace with the intent to showcase the inside of the flats as far as I can tell, it seems they had the permit to build it before the building existed.
And, as I understand it, it was the Tate's initial failure to do anything to restrain their visitors that caused the Supreme Court to decide as they did.