First, the article you posted: I've seen it before, written by a man named Tim Bolen. Mr Bolen and I have actually corresponded, and in that correspondence, he threatened me physically. He is a huge supporter of the theories of one Hulda Clark (you may look her up on quackwatch, as well). She has postulated that the cause of ALL cancers, as well as AIDS and a number of other diseases is a liver fluke. She claims that if a cancer patient will come to her clinic in Mexico, she can cure them of cancer, no matter how advanced (for a substantial fee, of course).
Next, Barrett does not think all chiropractors are quacks, but there are a goodly number of them who are. They believe that the cause of ALL disease (including cancer, diabetes, and others) is malalignment of the spine, and of course only THEY can cure the ill.
There is a great deal of quackery out there, but Barrett isn't part of it. He makes the entirely reasonable request that if you believe you have a magic cure for anything, demonstrate it. Show, in a controlled study, that your cure is better than what is out there now. If you don't want to submit your cure to a study, well, there must be a reason.
You can choose to believe anything you want, but if you try to convince your patients that "you know a better way," then you are violating the ethics of nursing practice (and may be practicing medicine without a license). Don't reject everything, but at least have some standards of credibility.