Mind you all,
tiny black holes are safe and occur in nature. When this sort of article refers to a black hole like object, they mean a couple particles in mass total. At that size/energy the black hole evaporates faster then it can take in mass.
Black holes evaporate? Seems so, though a process called Hawking radiation particle/anti-partocle pairs appear randomly out of the ether everywhere. These short lived particle pairs pop-up and quickly cancel each other out, like waves on the ocean. If the black hole is small these particle pairs dissipate it's energy quickly.
Simply, like waves filling up a boat that is too low on the water.
The best reason to think this huge contraption is safe? Naturally the earth is hit every minute with cosmic ray collisions with significantly more energy then this device can produce. This device just creates an environment where we can study these collisions and learn from them.
That is, unless this particle collider is a doomsday device! hah hah hah
By the way,
my favorite improbable doomsday device is Ice Nine.
"A fictional water crystal that grows off of normal water and is stable at room temperature."
http://en.wikipedia.org/wiki/Ice_nine
But perhaps more dangerous could be a real ice that burns...
"Methane Catastrophes in Earth's Past and Near Future"
http://www.bautforum.com/showthread.php?p=661775
Some say the world will end in fire,
Some say in ice.
From what I've tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To know that for destruction ice
Is also great
And would suffice.
By Robert Frost (1874-1963) (Poem first published in Harper's Magazine, December issue 1920)