One, because science is structured such that even where a high probability is suggested (in this case XMRV is not a pathogen), until the null hypothesis (in this case XMRV is a pathogen) is demonstrated to be false, scientists to accept the null hypothesis as having a degree of validity. There is a fundamental difference between saying "research on XMRV as a pathogen at this time is not an effective use of resources" and saying "XMRV is not now and never could be a pathogen". And two, because there is no way of knowing what other viral agency may be currently affecting someone with an illness of unknown aetiology, nor of what future susceptibility that individual may have, nor of what communicability any resistant organsm may have.
This may well be how science is supposed to work but all the evidence suggests that adherence to the scientific method very much depends on the interests of those involved.
The 'null hypothesis' that ME is caused by an as yet unidentified pathogen and has significant associated pathology has not been disproven beyond all doubt. In fact the balance of evidence to date suggests that the null hypothesis is valid. If science worked the way you suggest ME could not be classified by some as a psychosomatic disorder; ME patients would not be considered by some to have 'maladaptive illness beliefs' and graded exercise would not be recommended as a treatment when the extent of pathology is unknown and there is strong evidence suggesting it may cause harm.
Of course we don't exist in this ideal world.
The issue was the frequent warning to avoid ARVs not whether continued XMRV research is cost effective, although with regards to the latter, while the XMRV as pathogen null hypothesis remains valid, any right headed analysis could only conclude that the potential risks of not fully researching a novel human retrovirus far outweigh the costs, particularly when, as seems to be largely the case, XMRV research is not diverting funds away from existing ME/CFS research budgets.
Which gets us back to what I and others have been saying. The numbers of ME patients taking or who may take ARVs are miniscule and the frequency and stridency of the warnings against completely out of all proportion.
As for other viral agents; future susceptibility/transmission this is true for any member of the population yet doesn't seem to be a concern when ARVs are prescribed prophylactically - in numbers many orders of magnitude greater than the very limited numbers of ME/CFS patients.
Is the prophylatic use of ARVs a major concern requiring repeated dire warnings?
Methinks as regards ME/CFS that they protest too much which inevitably leads to suspicion about other motives.
An easy way to avoid/allay such suspicions is to assume that the vast majority of patients are sensible adults and not make a major issue out of a very minor risk.
