You created your own argument here though, right? I can be an advocate for any of one million serious problems that our societies have. Should everyone go destroy art galleries? Housing crisis = art destruction? Unliveable minimal wage = art destruction? Car centric societies = art destruction? Local store increased prices = art destruction? You have to agree that at a certain point this becomes indistinguishable from vandalism.
At what level then is this threshold? Or do you propose a hierarchy of ideas, which are suitable to protest in an art gallery, versus those that aren't?
The gallery still has to be closed, has to dedicate cleaners, invest into security measures etc. Vandalism can be as simple as spitting on the street. But that's not my point, in general.
My point is why mess with a place what has nothing to do with climate change, and not mess with places that absolutely do have something to do with it?