It seems laughable now but we should recall that when the Large Hadron Collider was being constructed, there were fears that the high-energy collisions it would enable would destroy the world by creating black holes or some such thing. Even I got questions about this possibility from people who are not normally paranoid.
I reassured them that the collision energies produced in the LHC would be nowhere close to the energies that happen routinely in collisions in the atmosphere due to cosmic rays. What the LHC would do is enable us to study collisions in a controlled environment as opposed to depending on unknown and unpredictable extra-galactic sources.
In this 2009 episode of The Daily Show, Jon Oliver interviews Walter Wagner who sued to try and stop the LHC. He failed. Wagner also tried and failed to stop another earlier accelerator named RHIC (Relativistic Heavy Ion Collider) that was built in New York state in 2000 to try and create plasmas that would resemble conditions in the early stages of the Big Bang. There were fears then that these collisions would create exotic particles known a ‘strangelets’ that might swallow the Earth.
(This clip was aired on April 30, 2009. To get suggestions on how to view clips of The Daily Show and The Colbert Report outside the US, please see this earlier post.)