I personally think doctors should be allowed to give placebos to patients in some circumstances.
Of course this is under the discretion of the clinician but if the patient is presenting symptoms which require no treatment at all yet the patient is insistent on receiving something, I believe it is far better to give a placebo than potentially contribute to antibiotic resistance or unwarranted side effects typically associated with psychological drugs.
Studies have shown the benefit of placebo drugs; don't discount the power of the mind. This is especially true when you consider disorders of the mind.
Perhaps I'm in the minority, but IMO, it is not unethical to give a sugar pill to a patient. Besides, better than than to have an angry patient complain about your practice for no good reason at all, especially given the current system is being setup on 'patient reviews'.