Ideology is never an accurate or complete description of the world. It is false awareness. What might be true under paradigm A might no longer be true under paradigm B, but at no point will an ideologue change his world-view to fit paradigm B. He will try to cram paradigm B into his ideology in order to preserve his ideology, rather than adjust his ideology to describe paradigm B.
For instance a fiat currency heavily regulated by state monetary policy might have been the best idea in the 20th century, during which for the most part there was no Internet. But in the 21st century, where the Internet enables markets that can function more efficiently, a virtual currency with a self-regulating monetary policy might be a better replacement. The jury is still out on that. BitCoin is an experiment, and that's the best thing about the Internet - it is a laboratory for experiments, where we can try new and different monetary policies really quickly, whereas in the wildly inefficient 20th century we were locked into one monetary policy at a time. We're just figuring out what works the best, but Krugman calling BitCoin "evil" suggests to me that he is afraid of what we might find out.