"The fact that nobody published a cheap way to double spend is strong evidence that it's difficult and expensive to double spend." Nonsense. Bitcoin is only a

"The fact that nobody published a cheap way to double spend is strong evidence that it's difficult and expensive to double spend." Nonsense. Bitcoin is only a few years old. It is not nearly well-studied enough to claim that there is any good evidence that double spending is costly. Keep in mind that in the first few years of RSA, people thought that 128 bit public keys would be sufficient for centuries. Bitcoin has not received anything close to the attention RSA received from the research community, or even that attention given newer ciphers like AES. "Also it doesn't really matter if there is some obscure method to cheaply double spend" That is kind of like saying, "It does not really matter if there is some obscure method to crack RSA quickly." "since because of its obscurity it would only affect a small number of transactions (and presumably once it is used it will be detected and made public, at which point it can be fixed)." Or it might turn out that there is no fix and that the attack would work no matter what you did to Bitcoin. Maybe not confirming transactions is an inherently insecure way to do business. It is equally possible that cheap double spending attacks are impossible due to some property of Bitcoin. Right now there is no clear answer; you just have to shrug and hope for the best if you neglect to wait for confirmations.