Well, as well as the guy stealing diamonds there's the guy above who trashed someone's stairs for no reason, the other guy who decided to trash a chest for reasons known only to himself, how many people are "good" really?
When I first spawned I took two trees (there were five in total) from outside someone's door because there was just no wood anywhere else, but after chopping them I planted saplings on the squares I took the trees from. That's being considerate, not "I wanted a chest but because I'm nice I took someone else's that only had cobblestone in it".
If it really was an emergency, why not build another chest and put the guy's cobblestone back in it?