But the art is never damaged. The pieces on display are in protective displays designed to weather a lot worse than food or glue. Not only that, they are often just replicas of pieces rather than the originals. Your point hinges on you being (actually) deprived of something, when you are not.
This is intentional - you are (figuratively) deprived of something to highlight how others have been deprived by the actions of the fossil fuel industry.
Assuming you mean Rodger Hallam? I don't want to ascribe malice but how well can you understand him if you got his name wrong?
I may disagree with XR and JSO out of principle but pretending like Hallam's comments are a declaration of war is absurd. He clearly feels that the poor are already the victims of class warfare and sees their actions as a justified response. It's clear to me he sees people like you and I as part of the ignorant masses, oblivious to the path of destruction the fossil fuel industry has carved through the lowest stratas of society.
Read my first comment.