The main issue is, I think, that in a situation like this, the photographer can appear to some people as a VISIBLE potential blip on the moral radar. An armed and dangerous one.
In other words, anybody who feels that some line is being transgressed when someone raises a camera towards them or the perceived "victim" has someone they can point at and say "that person is out of line / breaking the law / acting inappropriately / whatever". The photographer's defense is either to argue or discuss the point, continue regardless or walk away. I walked away because I had the shot and I didn't at that moment feel like talking to her about her point of view, as I sensed it wouldn't have made much difference and I wasn't in a particularly confrontational mood at that time. In some ways though, I now somewhat regret not bringing it up with her when I saw her and the students later.
There are laws that prevent the capture of photographs of people without there consent, but these didn't apply on this occasion.
If I had have been just some guy (and there were others) standing back and looking past the students to the sculpture, it probably would not even have occurred to the lady to say anything. Nor, even if it did occur to her, would she have had any grounds to confront me ("No - you can look at this statue but not past the students"????). Aha, but throw the evil contraption that can capture souls into the equation, and you suddenly have a potential creep stealing images for God knows what purpose and thus a reason to stand on your moral soapbox.
To me, this was just a promising picture opportunity and once I recognized it as such I busied myself with the logistics of getting the shot. Part of that decision was that the students would have their backs to me from my shooting point so there would be no ethical issue.
The fact that the authority figure pointed and said "No" and then carried on with a bunch of bs to the students didn't overly worry me because I knew I was on steady legal/ethical ground, had done no wrong, and already had the shot I wanted.
I like the idea of insisting she move the students and chairs though! Ah well, next time...