The authors are right to say that physicists can get cliquish; that some of them swagger; that they frequently fool themselves and that science has become too risk-averse. On the other hand, dozens of astrophysicists, cosmologists, relativists and people who study fundamental particles and interactions in ways not related to string theory do quite nicely; some even dip into theory now and then. In fact, many highly esteemed physicists who formerly disdained string theory (Nobel laureates Steven Weinberg and Murray Gell-Mann among them) have become fans.
So it's hard to believe, as both authors charge, that physicists have been led like sheep to pursue a "failed theory," mostly by Edward Witten, now at the Institute for Advanced Study in Princeton and generally acknowledged genius -- and also a nice guy. (In addition to his multiple prizes in physics, Witten also won the Fields Medal -- the "Nobel Prize" of mathematics.)
True, Witten is highly influential. But it's hard to imagine him ruining an entire generation of physicists. They are not, in general, followers; getting them to agree on anything is like herding cats. They love nothing better than to prove each other wrong.
The claim that string theory can't be tested is serious; experiment is the ultimate arbiter of truth. But it's impossible to know what is ultimately testable. When the ghostly neutrino popped up in one of Pauli's equations, the physicist admitted he'd done "a terrible thing. I have postulated a particle that cannot be detected." Then in 1956, traces of neutrinos were seen in the wash of radiation spewing from newly commissioned nuclear reactors.