[frogpelt]

If someone could do this without being caught what would stop someone else from doing something sinister and deadly? That's how I took it.

[lotsofmangos]

People have always been able to do sinister and deadly things. The reason that they do not happen more often is largely not because of people stopping them, but is rather because not many people are really that nuts.

The ability of pranksters to switch flags on a bridge does not make your world more risky. A heavy handed state triggering paranoid reactions from the mentally ill may well do.