What makes people believe they are the ethics police?

I was at Wal-Mart today. I was at a closed register. I was leaning over the revolving belt thing reading a magazine. Anyway this woman who didn't even work there came up flipped the switch and sent my elbows skidding and my magazine down the belt. Then she just turned around to bag her groceries like nothing happenned. I was totally outraged I thought what a friggin *****. I mean I was probably gonna buy the friggin magazine and even if I hadn't what would have been so horrible about me leaving the store with some knowledge of headthe ledger? It wasn't like I was stealing it? My point is what makes people think they can just into other peoples business like that? What makes others think they can force their ethics on them?