Doctor: While a few alternative medicines have dangerous side effects, some, such as many herbs, have been proven safe to consume. Thus, though there is little firm evidence of medicinal effect, advocates of these herbs as remedies for serious illnesses should always be allowed to prescribe them, since their patients will not be harmed, and might be helped, by the use of these products. Which one of the following, if true, most seriously weakens the doctor's argument? ['Some patients may have allergic reactions to certain medicines that have been tolerated by other patients.', "Any pain relief or other benefits of many herbs have been proven to derive entirely from patients' belief in the remedy, rather than from its biochemical properties.", "The vast majority of purveyors of alternative medicines are driven as much by the profit motive as by a regard for their patients' health.", 'Many practitioners and patients neglect more effective conventional medicines in favor of herbal remedies.']