Will no one rid us of these turbulent ratings? Years after misjudged ratings on mortgage-backed securities helped cause a financial crash, credit ratings firms are still embedded in the system's plumbing. Regulators should be trying harder to remove them from their rule books.

Using ratings in this way tends to assume that they are largely static or slow-moving. When they prove not to be, unexpected consequences abound. One recent example is Fitch's decision to strip France of its triple-A rating.