Well, some did not alter their trajectory, and took to it with sledgehammers to and defied it's ability to be a wall.
Exactly right: everyone, even the sledgehammerers, agreed there was an "it" that needed to be defied. If, prior to 1989, an East German were confronted with the oppression of the Berlin Wall and someone said to him or her, "Don't worry. The Wall doesn't even really exist outside of our experience of it," I'm guessing they would not be mollified. I'm guessing they would find it convenient to assume, even if temporarily, that there really was an obstacle of bricks and mortar to be the target of their sledgehammers, and that the wall should come down not only for the sake of their own personal experience but for the sake of anyone else who might not necessarily have been experiencing it at that moment. You know, just in case.
Yes, we all act as thought the wall is objectively "there", but only by consensus.
A very strong consensus, yes. Again, find me someone who doubts the existence of a brick wall right at the moment they are about to crash into it, and I'll take seriously the notion that reality is not objective.