I forgot to mention one of the points I made to the two scientists I talked-to about the Large Hadron Collider.
It was a one-word argument: Tunguska.
They argued that cosmic rays from space -- 90% of which are extremely-high-energy protons, similar to what the Collider will generate -- don't cause a problem on Earth, so why worry?
In response I said, "Tunguska."
In 1908, the largest explosion in the history of the world -- some estimates are in the 100 megaton range -- flattened a vast, vast area of Siberia -- about 1,200 square miles.
The impact point was very obvious -- trees radiated away from the impact point very revealingly.
But, there was no crater. Just a little lake.
In any event, Tunguska is probably the best candidate for being the event when an incipient mini black hole passed through the Earth.