For what it's worth, most of those JSO protests have been done in a way that would not damage the actual object. Like the Stonehenge one, it wasn't paint, it was cornflour and food colouring that would just come off in the rain (and was, in the end, removed with just a leafblower). The Magna Carta one actually was doing damage though.

Regardless of that, I don't personally think that they are effective protests. They're far too easy to frame as mindless vandalism.