In the summer of 1945, as the United States prepared to detonate the first nuclear weapon in the American southwest, several scientists on the Manhattan Project team, most notably Edward Teller, expresseed concern that the kind of fission reaction utilizied to trigger the explosion may not be containable. What Teller and the others feared was that the reaction would spiral continually, growing larger and exponentially more powerful (all within microseconds), and eventually ignite the planet's atmosphere. After debate, the team agreed that this was a possibility, albeit a very small one, but decided to move forward with the test as planned.
Obviously, the Earth's atmosphere survived. However, a very important ethical lesson can be drawn from this: Mankind will try anything once. One of these days, once is all it's going to take. Case in point: not satisfied with the strength of the first two nuclear devices deployed over Japan in August of 1945, the United States got right to work inventing larger, more powerful nuclear weapons. Edward Teller himself, obviously relieved of his fears of world annihilation, went on to invent the hydrogen bomb, exponentially more powerful than its predecessor.
As the video clip above points out, the Large Hadron Collider presents science with another risk / reward scenario, this one containing even more potential for unwanted disaster. This time, though, instead of approaching a frontier with a 'best guess' attitude of gauging the probable outcomes (a la those on the Manhattan Project, who had no hard data either way), scientists working on the LHC are working within the framework of the Standard Model of Physics, which, despite what they say about the specifics on black holes and supersymmetrical particles, does provide strong data that the fabric of spacetime will be stretched to its limit, so to speak, when these collisions occur. The reward to be gained is the completion of the Standard Model of Everything, or a completed Grand Unified Theory, as explained in the clip. Attaining this knowledge will allow scientists to define our universe with a single set of fundamental laws and values. This would allow for the expansion of our knowledge of the universe around us to expand exponentially, pun intended. Hopefully, though, one of the lessons we will not learn from this new set of rules is "never collide two protons at 99% of the speed of light."
Albert Einstein's Theory of Relativity is the real wild card here. This is the model that has many scientists worried. Einstein's Theory would, in this case, point to the creation of these micro black holes that, being caused by release of energy from a single point in spacetime, would be stationary. Most theories regarding stationary black holes leads to them growing. That's the big risk in this case. There are also other, less disastrous, and even quasi-comical potential side effects, like the creation of CTCs (closed timelike curves), and the theory (presented in this article in the U.K.'s Telegraph), that we should look forward to welcoming time travellers when the LHC is switched on in the coming weeks.
There are times it seems that humankind's search for knowedge resembles that of a child crawling along the floor, constantly needing an adult to warn "Don't put that in your mouth." In reality, though, we are neither the adult (coincidentally, the Higgs boson is referred to by most as the God particle) nor do we seem intent on listening. Humankind's propensity for the bigger, faster stronger, more attitude leads one to suspect that if unsuccessful in this endeavor, manknind will surely find - to mix metaphors - somewhere else to stick his finger.
For the record, Albert Einstein disagreed with Edward Teller's concerns about runaway fission in 1945. He was right that time, let's hope his theory is wrong this time.