Not an expert myself, but I somehow doubt there was only a single study showing the effectiveness of placebos. It's a very common subject and a key component of current scientific testing (control groups).

It's better than nothing!

The author didn't seem to refute that placebo with some amount of deception could have moderately significant positive effects on subjective diseases such as pain / depression. Not that alternative medicine is ethical due to that, but simply that having a strong doctor/patient relationship may be almost as good as prescribing drugs in some scenarios. Or subjective measuring just sucks and some diseases have to rely on it so the measurement is affected more than the disease.

Objective diseases are a whole other matter.