Let me answer all of these at once. The LHC has absolutely no chance of destroying anything bigger than a few protons, let alone the Earth. This is not based on theoretical assumptions.
It is, of course, essential that all scientific research at the frontiers of knowledge, from genetics to particle physics, is subjected to the most rigorous scrutiny to ensure that our voyages into the unknown do not result in unforeseen, perhaps dangerous outcomes.
Cern, and indeed all research establishments, do this routinely and to the satisfaction of their host governments. In the case of the LHC, a report in plain English is available here:
http://public.web.cern.ch/public/en/LHC/Safety-en.html
For the record, the LHC collides particles together at energies far below those naturally occurring in many places in the Universe, including the upper atmosphere of our planet every second of every day.
If the LHC can produce micro black holes, for example, then nature is doing it right now by smashing ultra-high energy cosmic ray particles into the Earth directly above our heads with no discernable consequences.
The overwhelmingly most likely explanation for our continued existence in the face of this potentially prolific production of black holes is that they aren't produced at all because there are either no extra dimensions in the Universe, or they aren't set up right for us to see them.
If black holes are being produced, then next on the list of explanations for our continued existence is the broad theoretical consensus that sub-atomic black holes should fizzle back into the Universe very quickly, billionths of a second after they are created in a little flash of particles via a process known as Hawking radiation.
In other words, they evaporate away very quickly indeed. This process, which is perhaps Steven Hawking's greatest contribution to theoretical physics, is on significantly firmer theoretical ground than the extra dimensions theories required to create the little black holes in the first place.
Even if Hawking is wrong, and therefore much of our understanding of modern physics is also wrong, the little black holes would be so tiny that they would rarely come close enough to a particle of matter in the Earth to eat it and grow.
And even if you don't buy any of this, then you can still relax in the knowledge that we have no evidence anywhere in the Universe of a little black hole eating anything - not just Earth but the Sun and planets and every star we can see in the sky, including the immensely dense neutron stars and white dwarfs, remnants of ancient Suns that populate the sky in their millions and which because of their density would make great black hole food.
So - the only theoretical bit is in the proposition that you can make little black holes in the first place. From then on, observation tells us that these things either (a) don't exist - the most likely explanation; or (b) exist, but do not eat neutron stars and are therefore harmless, probably because they evaporate away very quickly indeed!
I am in fact immensely irritated by the conspiracy theorists who spread this nonsense around and try to scare people. This non-story is symptomatic of a larger mistrust in science, particularly in the US, which includes intelligent design amongst other things.
The only serious issue is why so many people who don't have the time or inclination to discover for themselves why this stuff is total crap have to be exposed to the opinions of these half-wits.
