gmaxwell put out a recent and good discussion on this, in regards to this topic here:
https://bitcointalk.org/index.php?topic=946236.msg10369307#msg10369307Though he calls it the "inherent cost of transactions", this is the bitcoin network's fundamental cost and value added for if there are no transactions ever again, there is not any more meaning to Bitcoin.
What sort of demonstration are you seeking? Why is this in doubt?
He seems to simply be asserting it without actually backing it in any way.
If taken for granted it actually weakens the hardforkers' position.