What makes bitcoin unsustainable? The fact that it will some day stop rising in value?
No. Reread Impaler's post. What is unsustainable is that transaction fees are rising rapidly, but that at the same time they are unable to cover network costs.
But - the second graph doesn't mean a lot by itself, we need to see transaction fees as a percentage, not as a dollar figure- and even then what's interesting is the median, not the average.
https://blockchain.info/charts/cost-per-transactionThe actual average fee per transaction is around $0.30 (divide 'total transaction fee' by 'number of transactions' here):
http://blockchain.info/statswhat's scary is the electricity cots - $11 mil per 24 hrs??
EDIT: the electricity stat is BS. I'd estimate total cost at around $150,000 per day. Don't know why they publish this? Do they want to make it seem that mining is not profitable?