-Raeky, being a professional in a related field does not give an editor a COI, otherwise MDs could not edit medical articles and dentists could not edit dental articles, etc. If you disagree, please indicate which category of COI you feel DVMt belongs to and take your concerns to the relevant noticeboard to get consensus and set a precedent at wikipedia for editors editing articles related to their profession. Otherwise, please keep your comments here specific to the text and sources and not about other editors, ie., remain WP:CIVIL. 
-What needs to be established here is if the few sources that are 'against the grain' and are highly critical of the efficacy of manipulation are noteworthy or simply represent a WP:FRINGE view. IMO, Ernst & Podsanski are the only 2 authors who make bold statements about manipulation, such as 'not effective', whereas the bulk of sources suggest equivalency with usual medical care and other conservative options. Thus, I see Ernst & Podsanski as outliers, or fringe, with regard to this specific topic of manipulation for back pain. Even source #4, which you noted says equal to sham, still suggests equivalency with other therapies for back pain, including usual medical care. 
-Doc James, you seem to want to omit the common finding by multiple high-quality sources that manipulation is equivalent to usual medical care and physiotherapy for back pain? Doesn't policy indicate that the majority view gets more weight? Which theme has more weight among the available secondary sources? 1) That manipulation is not effective for back pain or 2) that manipulation is equal to 'usual medical care' for back pain? I think that we will need to decide how much weight each idea should get....hopefully this RFC will help. Also, you say you like the current text, but how does the current text "may be as effective as other manual therapies" reflect the well-sourced fact that manipulation is also equivalent to usual medical care for back pain treatment?