What would a Higgs at 125 GeV tell us?

* Triggering the collapse of the vacuum to a more stable state

* Production of strangelet particles that convert everything to more strangelets

* Production of microscopic black holes that eventually swallow the Earth

First of all, all three require hypothetical extensions to currently accepted physics, but the most compelling argument against these being possible is the fact that thousands and millions of times more energetic events than what LHC is capable of occur all around the Universe all the time, including in Earth's upper atmosphere, and we're still here.

See http://user.web.cern.ch/public/en/LHC/Safety-en.html

Note that if LHC was capable of this, it would have already happened. Ultra-high-energy cosmic rays are detected occasionally, and statistically, they hit Earth more than once per day. The highest energy ever detected was a particle with 3*10^20 eV, or 300,000,000 TeV, or roughly as much kinetic energy that a baseball has at 60mph, in what was likely a single proton. It was aptly named the "Oh-My-God particle".

[ps an example of how simple arguments are not necessarily right is that any black hole created by the lhc would be almost at rest in the frame of the collider, unlike expected products from astronomical processes; that means that it would be gravitationally bound, allowing the effects of a small cross-section to accumulate over time. this isn't advanced physics, by any stretch of the imagination, yet people never seem to address it. another issue is that planets may indeed be destroyed by cosmic processes - at the time the lhc was being designed we had very little in the way of statistics on the number of planets or their lifetimes, outside of our own solar system.]