One reason you will never prove that the sarsens could not have been dragged to Stonehenge is because they could have been dragged to Stonehenge. Whether they were is a totally different question :-)
My personal view is that they scale of Stonehenge as opposed to the Great Pyramid for example does not mean it was a necessity to do it any other way. Erecting them with A-frames rather than levers is, once again, a different matter.