Particles collide all the time. Cosmic rays from the sun are crashing into the earth every day. There haven't been very many black holes created in the atmosphere.
What I'm more afraid of, is the fact that the temperature of those particle collisions reach 100,000 times hotter than the center of the sun. That's fucking hot. In fact, that's hot enough that if there's a malfunction in that tube of theirs, the earth is going to have some serious issues.
Also, there's some theory that if they create the Big Bang all over again, it could mess with the instability of the universe and create a vacuum bubble, which would destroy the entire universe.
But no worries, the French are in charge of this project. They never fail.