So, you want them to assume that neither the transaction fees nor the exchange rates increase in the future? Huge coincidence that both of those assumptions favor your side in the debate?
"To assume is to be deceived." (Yiddish proverb)
I wouldn't want anyone to assume anything. Just saying that 99.8% of current total hashing power is payed for by the temporal generation of 50 bitcoins per block. And that it would be reasonable not to take these into account if (normal) bitcoin operation is discussed.