Well
To the naysayers, I say:
There's an entire universe out there. The human race occupies approximately nothing of it. Seriously, so small as to be completely, entirely insignificant. And in terms of mass/energy, we really are using *nothing*.
Even if we could harness the power of the entire planet, or even solar system, and focus it onto warping space and doing other tricks, we aren't going to destroy the world accidentally. There might be a big bang at the LHC in the conventional sense (smoke, flames, loud noise) but we're not going to be kick-starting the second Big Bang from the Starbug's engines.
If we could, we'd be witnessing Big Bangs and self-created black hole all over the cosmos and they would be our primary indicator of "intelligent life". And if we could do that, we'd still be an insignificant speck compared to the civilisations that manage to survive *their* "LHC era" and move on to the next "theoretically-safe" experiment. But if we don't at least try, we might as well have stayed in caves eating cold veggies because we had no tools to hunt or cook with.
It's actually a factor in things like the Drake equations if you do it properly - scientists take account of the fact that any intelligent civilisation might well do something daft and blow itself to pieces. Personally, I think the sword or bullet would prove to be a much more devastating invention to help that along without the need for advanced scientific research on it.