A question about ducks and cairns

[OldnSlow]

A group of us hiked Whale Peak in Anza Borrego yesterday. On the way down from the peak we ran into a rather unfriendly hiker and we noted he was knocking down every duck and cairn he went by. These had been really helpful to us on the way up, it's quite the scramble and not really well marked otherwise.

When we asked him why he was doing that he angrily said it is the code of leave no trace and these were graffiti along the trail.

I'm not sure I've encountered that attitude before, and I always thought they were a pretty natural way of keeping us all on a single trail rather than fanning out over sensitive wild lands.

Is he right?