When you 're a sculptor and you hear people are bringing down statues.
Joking apart, here's where I stand as an art creative. Public art's duty is to allow itself to be affected by the social and political processes brought in by all eras. Why? It's in its job description. And that influence does get physical. Our monuments are like the palimpsests our streets are. Interventions however should not be destructive to the work's form, so that future generations won't be excluded from the discource.
We must distinguish the two forms vandalism takes: People's activism and not. Public vandalism by the community is a valid act. Covert vandalism is arbitrary. It being non-democratic is not acceptable, also everything brough upon art for the mere joy of destruction. I have many examples for all three cases in mind.
Portrail sculptures, on the other hand make a separate category. U.S. President Truman's statue [a controversial Athens monument demolished several times and even blasted] is to the public Truman in person. Some artists respect that. We too must be tolerant of destructive vandalism because it addresses not the artwork itself but it's off-image. Of course with the exception of works that is of archaeological value.
To me every kind of action/intervention on public work of art is art. The police squad that guards 'Truman' day and night; art. The slave trader to dive in the Bristol port; art.
I consider public art to be one of the most authentic genres of political art. This is because it contains the gesture of the artist and the whole spectrum of political life from the first day of publication until today. One arrives in a new town and in public art, formal and informal, one can see it's present.
If I fail to see the present, something's not alive. Either the art or the community.