I seriously doubt the authors said herbal medicine was scientifically impossible - in fact judging by the overview of the book presented here, the authors seems to acknowledge that herbal medicine do work (in contrast to the other examined treatments).
Homeopathy has been and will always be bullshit. If you dilute something beyond Avogadro's number, its gone. There's no "water memory" or whatever people have been trying to claim for years.
At best, if you REALLY believe homeopathy works, you will benefit from the placebo effect. However, most logical sane persons when explained what actually goes on in homeopathy will NOT believe that it works and hence they will not benefit from the placebo effect.
I apologize for not clarifying that vaccines are NOT diluted beyond Avogadro's number - there is actually an active ingredient in a vaccine, as opposed to homeopathic remedies. My mistake. Homeopathy is definitely not and will hopefully never ever be a part of "traditional medicine", not are any "big pharma" companies selling anything that could be just remotely though of as a homeopathic treatment. I will guarantee you they would be out of business / sued out of existence before you could say QUACK :-).