I would probably never trust an herbalist over a physician, but that's my opinion. I would wonder what is the education behind what this herbalist is saying? Does he have extensive knowledge in botany? How about pharmacology?
Think about the plant foxglove. It is used to make the medication digoxin. A very important medication used in treating certain cardiac issues. While I don't know anything extensive about foxglove, perhaps a botanist would know something valuable the plant in its natural form may have unwanted side effects. The biggest problem with just eating an herb, is that many are not regulated by the government and may contain impurities that while you are trying to get the desired effect (say cardiac treatment from the foxglove) you are also getting unwanted side effects that can be eliminated through extracting the desired chemicals only.
I would also expect a pharmacist (at some point in their schooling) to learn about more of the plant origins of medications. Whether or not they remember all of them is another story.
Also, there's a misconception about herbs being "natural" so they are somehow not harmful. This is simply not true. Tobacco is natural, marijuana is natural, there are many plants and herbs that are found in nature that would kill you if you ate them. The reason I would always trust a medication over an herb is first, its controlled. It was made in a lab, and we know what went into it. Second, its been studied, including its adverse effects. Herbs don't come with a list of all the possible side effects you may have due to using it. Third, medicine has a better chance of actually working. If an herb truly had this magical healing component, than medical researchers, pharmaceutical companies and everyone in between those two would be itching to study it and get in made into an excepted treatment. Some might be motivated by money, others by concern for patient welfare, but trust me, if an herb really was proven to be effective, it would not continue to stay this untapped resource.
I think the biggest reason people are afraid of convention medicine and turn to people like herbalist as their only approach (as opposed to patients I have had that follow conventional medicine but still use other forms of healing, and they do inform their doctors of such) is that people do not fully understand the science or medicine behind what a doctor says or prescribes, and they feel powerless, which make them feel they are being taken advantage of or lied to. (Like the crooked mechanic fear) Lets face it. There's not a ton of schooling behind medicine for no reason. They learn a lot that lay people just aren't going to learn with out sitting through the chem, bio, anatomy and physiology, the pharm classes. You can read a lot, but that type of knowledge foundation comes from formal schooling. So, we are forced to trust our doctors when we listen to their orders in circumstances where we don't have the knowledge or understanding to make the decisions on our own. We are trusting that they have our best interest at hand, and weren't the "C" student in med school. I think this scares a lot of people. I know this scares my dad, and he is pretty much anti medicine because of it, and his daughter is a nurse!
Also, I think the other issue is doctors expect patients to take more self responsibility. A doc is going to tell you, to manage diabetes, aside from the meds, you need to eat right, exercise and lose weight. Some people don't like to hear those types of things. They get angry at the doc for being rude or heartless. But the herbalist who is more likely to say "take this" is appealing to our egos. He doesn't point out what we've done to contribute to the problem, and he's not asking us to take the difficult steps in our own lives to correct it.
I remember when my cousin had trouble conceiving, and she must have went to every OB in the county. She complained that the docs continued to recommend she lose some weight before she tried to conceive (and that it would help her chances). She is morbidly obese. She even walked out on a doc because he said he would not address her infertility until she lost some weight. And she'd call me and complain that the docs had no right to put her on the spot about her weight. She wanted to keep her head in the sand and a good doc will make you take it out. Well, after many docs she found a doc (crappy one as far as I'm concerned) that just feed her what she wanted to hear, NOT what was in her best interest as a patient. Put her on what she needed to be one and she eventually got pregnant....and had gestation diabetes and some of the thankfully less threatening complications that came along with it. And when I asked her if she plans on now trying to lose the weight before her next...she was insulted I should suggest such a thing. She is someone who think all docs are out for her money or are heartless jerks, which is easier for her to admit than to step up and say "yes I need to loss weight before trying to conceive".
I could tell thousands of these stories related to smokers, alcoholics, people of an unhealthy weight (and that can be over or under), people that tan, that abuse steroids, and everything in between. People that would rather hear an herbalist say "take this" and our problems are "toxins" related to all the "impurities" in our world today. Its the drinking water, the air we breath, the processed food we eat, but its not anything you did. I'm not saying that there aren't contributing factors out there in our world. What I'm saying is when I get someone who smoked 2 packs a day for 50 years (and is still smoking) tell me they are worried about getting cancer from the tap water!!!! Or a microwave (this is a true story) I'm just floored at that kind of denial. Or they are worried about the "toxins" the drug companies "want to put in our bodies" while they are still smoking! I've noticed in my patient experience the more in denial someone is about their own contribution to their bad health, the more they don't like docs and would rather go to someone like an herbalist or whatever. I'm not saying this is true for everyone, just seems to be more often that not.
We all make mistakes. Heck, not only to I know the damage I'm doing to my body being over weight (actually I'm clinically obese, which I wasn't before I got pregnant, but pregnancy is no excuse to gain so much weight) but I've seen what it does to the human body. I know if I don't get this weight off, I'm going down a path to type II diabetes. (And I will not TTC again without losing weight first) And I don't want a guy to tell me to just take this vitamin or that herb. Because where is he going to be in 20 years when I'm a diabetic? He'll be gone and it'll be the doctors that will be trying to keep me from loosing my feet or fingers, losing my eye sight, going into renal failure and everything else that diabetes can result in.
Wow, that was long. But I have free time right now. I'm basically just sitting here waiting to go into labor!