Black Rocks is very popular with non-climbers, so it may well be someone with no idea that what they are doing is damaging and affects other people. A few years back, I was near Angel's Share. To my horror, I heard the "tink tink" of hammer and chisel from around the corner. I rushed round, full of self-righteous anger, only to find 2 small boys and an elderly gent, hammer and chisel in hand. I managed to calm down and explain that chiselling away might not be a good idea becuase of the effect on climbing, and it was totally obvious that such a thing had never occured to them.