The article ignores incentives - that the effort in trying to find a new block may be better than the double spend. You'd have to buy a big ticket item, and get

The article ignores incentives - that the effort in trying to find a new block may be better than the double spend. You'd have to buy a big ticket item, and get really lucky as well so you have a fairly small window to catch up and get head. So bitcoin works partly because the incentives to be an honest member outweigh the potential benefit of attack vs the cost and risk of simply not winning in the window within which you can double spend. I'd consider some of the other uses of block chain such as permission-based approaches, and the other applications like luxury goods in supply chain to prevent counterfeit goods from entering.