In my opinion, physicians are no different from any other profession. They feel that input from those outside the profession on matters of the profession are irrelevant, and in most cases this is probably true. There is a push in the evidence-based medicine movement, however, to recognize the influential power physicians have in the doctor-patient relationship and the ways this influence might effectively ignore the patient and their right to dictate their own treatment path. It's called "Informed Patient Choice," and is something I personally believe should be emphasized much more than it is today, because the truth is for most diseases there are multiple treatment routes, each with its own advantages and disadvantages. The job of the physician should be to, without bias, present these options to the patient and ultimately allow them to choose.
As for dismissing alternate treatments, I feel it's perfectly acceptable to dismiss treatments that lack basic scientific validity (Mind you, I include in this bunch treatments prescribed by physicians today that lack proper evidence, of which there are more than a few). There are an increasing number of physicians interested in CAM, however; some hope to discover new medical treatments hidden within; some use them as a rich source of evidence related to the placebo effect; or, as was mentioned earlier in this discussion by another poster, some seek to stake their share in the increasingly lucrative market of quackery.
The truth is, quackery is even more lucrative than medicine. All that is needed is invention of a treatment that doesn't hurt people, at least not immediately (Think water soluble vitamins, fruits, vegetables, etc...), and clever marketing. No grants need to be written to conduct the basic science research. No costly clinical trials need to be conducted. The FDA doesn't regulate "alternative therapy" because most are categorized as supplements, and so efficacy data does not need to be provided. All of that costs a great deal of money, which of course eats into profit. In addition, as proponents of CAM can't point to a single treatment that has been effectively "taken off the market" due to lacking efficacy, it's quite clear that not only are these treatments 100% quackery, but they hold amazing long-term revenue potential, Potential that exists because patients are taken advantage of and claims are made by peddlers that aren't supported by a shred of evidence.