Should everyone go destroy art galleries? Housing crisis = art destruction?
Do you not agree? Over half a million homeless are without homes. People are dying, and the homeless are largely being dehumanized or ignored. There is a very real human cost far beyond a piece of art or the barrier protecting it.
If you're looking for objective quantifiable criteria on right vs wrong, you'll never find it. Morality often falls into a grey area involving tradeoffs, but bringing attention to a societal issue with huge human costs just for splashing soup on a plastic barrier seems pretty effective to me.
Less shock value -> less publicity -> less people thinking about your message