I’m not keen on that quote. It’s half-true and would potentially be quite misleading to people who suffer from anxiety disorders, I think, based on my experience. Anxiety serves that purpose in terms of evolutionary psychology, sure, but in anxiety disorders it’s become dysfunctional and we talk about it as setting off false alarms. The anxiety of someone with GAD or PTSD is not preparing them for real danger. It’s become overly-sensitive and is triggering false warnings of danger. Still we are better to accept the feeling but not to agree with the threat appraisal implicit in it, which is probably false in most cases.