CERN commissioned a study in 2002 on the possibility of dangerous objects i.e. micro black holes, strangelets
and er monopoles
being produced. It was concluded that 'there is no basis for any conceivable threat.'
They commissioned another study in 2007 because of further concerns raised. This was to be published in early 2008 but I can't find it so maybe it hasn't been published yet? Whatever the new study concludes, I doubt it would stop them going ahead.
I believe it was suggested that if stable micro black holes were created in the LHC, then they must be safe because the greater energies of cosmic rays striking the earths atmosphere and the moon would have been creating them throughout history and without consequence. However if naturally occuring stable micro black holes were being created by cosmic ray collisions they would have extremely high velocities so they would not be captured by gravity and would simply pass through the earth/moon too quickly to accrete significant matter. One concern that has lead to the second study is that stable micro black holes were created in the LHC, they would be dangerous because they would be too slow moving to escape gravity.