>This is the only coherent argument of this point that I've ever seen, and I thank you for it.
Ok, I too value that explanation, because it is the essence of the counterargument against the argument that allowing self-signed certs without warnings would be a net improvement.
But after a couple minutes of hopefully actually grokking this explanation of subsequent potential net-banking mitm attack vectors, this thought occurred to me-
Isn't the only added hurdle to pulling off this attack the need to get a non-self-signed cert? Which sure, is a bit of a relative pain and cost compared to a self-signed cert, but if you were mitm attacking peoples bank accounts, wouldn't getting a valid (effectively disposable) cert be just a 'cost of doing criminal business?'. Sure in the process of getting the cert, you have to leave some identity information, use a credit card, but in my estimation of current global security, I tend to imagine that the criminals could do those things effectively anonymously.
And if in the unlikely event that both my understanding of the issue, and that subsequent analysis are correct, then the question is- which is the bigger net gain for society- the benefits of facilitating easy https encryption with self-signed certs, or the benefits of adding the go-buy-or-steal-a-real-cert hurdle to bank attackers? And I think I'd lean towards the former. But odds are I'm still misunderstanding various aspects of this...