The pebbles on a beach help protect the beach from erosion. So you might be only taking one or two pebbles but if everyone took one or two pebbles the the beach could be washed away.
"if everyone took two pebbles"!!!!!!
Wouldn't it be more worrying that everyone may be acting very oddly, than the overall effect of shoreline erosion? It may also put those magicians out of work....you know, the ones who can tell you what you have in your pocket....