I think this thread could maybe be moved to "Hilbert" where such discussion belongs better. Anyway here is my 2 c.

I think physicists do not understand gravity at all, but that is not their job. Only God can understand gravity. But Physicists understand how gravity behaves which is not the same as understanding gravity. But they can describe and predict it very precisely.

Thats why they made experiments, for finding out how something behaves. Thats what they are very good in. Of course there can always be surprises in physics, but destroying the world with the large hadron collider is very unlikely. But there were always people who warned of such experiments, for instance there were warnings that landing on the moon could cause the rocket to collide with an invisible sphere between earth and moon and destroy the world.

So we must apply some common sense for judging the dangers and advantages of experiments. Finding the higgs boson is important and an earth eating black hole is extremely unlikely, so I say: Go LHC go!