Being both European and an artist I like the moral rights doctrine a lot, but I don't think it would hold any water here as Di Modica is attempting to extend his claim of authorship to the space around the Charging Bull, and essentially demanding that his art should enjoy the privilege of being viewed in isolation, ironically redolent of capitalism itself.
The boundary of a work is very important artistically, and there are all sorts of explicit and implicit conceptual assertions made by how it shapes the rest of the work. Di Modica chose not create an explicit border around the statue, not least because to do so might have changed its meaning - a ring, for example, would suggest that the bull should be confined, where his intention was to celebrate its vitality and strength. Where, then, is the boundary of a sculpture? At what point does something impinge upon it?
I suggest that the fair boundary of a free-standing sculpture is that distance from it which allows a human viewer to apprehend the work as a whole. The point of an art work is to create a unique sense impression in a person who encounters it, and size is a quality independent of individual sensory channels, but measured in relation to ourselves. In this case I feel that the distance around Charging Bull from which people can view the whole thing in unimpaired in any significant way.
People who feel the space around the sculpture has become a part of the work are equating the semantic content that the work presents with the work itself. The sense of power and motion in Di Modica's sculpture touches our instincts about how much space to give it. But those distances are personal, and exist in our psychic space rather than in real space. In real space, the only kind of distance over which one can speak of damaging an art work is by impairing the ability to view it in full. How people feel about Charging Bull is a personal matter, but it's misleading to conflate the experience of contemplating it from a given spatial point with the content of the work itself. We have become used to thinking of the sculpture as dominating the space around it, but the space is no more part of the work than the Louvre is part of the Mona Lisa.