So here's the thing. Just Stop Oil is performing symbolic disruption and vandalism. And they are doing it to exactly the targets you say they should - for example, Taylor Swift's private jet.
And they are also performing symbolic vandalism against works of art and history.
And I submit the way you feel about them targeting Stonehenge is very similar to the way a wealthy conservative feels about them targeting private jets - it offends you even though it does no actual harm because it's an attack on something you value and something you feel should be respected, which makes you feel like it's an attack on you personally.
Just Stop Oil has been very clear about why they symbolically vandalize works of art - because every dollar you spent on preserving human art and history is meaningless if the human species drives itself to extinction, and anyone who cares about art and history needs to get off their asses and demand political change. They do it because people who care more about art than the environment are the people they're trying to shake up and motivate.
Preserving art is a bourgeois luxury. If we as a species don't get off our asses and fight climate change we won't have any art left to preserve or any human beings left to appreciate it.