‘We’ve heard these same stale arguments before,” said President Obama in his speech on climate change last week, referring to those who worry that the Environmental Protection Agency’s carbon-reduction plan may do more harm than good. The trouble is, we’ve heard his stale argument before, too: that we’re doomed if we don’t do what the environmental pressure groups tell us, and saved if we do. And it has frequently turned out to be really bad advice.

Making dire predictions is what environmental groups do for a living, and...