[rmrfrmrf]

The problem with this argument is that you stop passing the buck when it's convenient for your argument, not to its actual conclusion. The only reality any one of us can actually be sure of is each of our own minds[0], therefore the only way to keep information secure is to never share it. Even then, our brains in vats could be under constant monitoring and decoding, therefore making secrecy a futile exercise altogether.

Because a solipsistic worldview is, perhaps, irrelevant to everyday life, we begin to operate on assumptions based on information that's infeasible for us to know for certain. This is what you must do to talk about security on the Internet: limit the domain of the problem by making assumptions about the Internet's infrastructure. You're right that it will never be possible to share a secret on the Internet without risk, that's not the point of this article or any others that indicate the flaws of JavaScript cryptography.

[0] http://en.wikipedia.org/wiki/Solipsism

[jerf]

When you've been reduced to arguing about brains in vats, you're no longer having a technical conversation about security anymore. We're talking about security here.