No, it's not a non-sequitur, as there is not good evidence of absence of every pathogen that could potentially cause ME, I would use Yersinia as an example, simply because I know that the standard test for this in the UK was found to be inappropriate for chronic cases in the 1980s...The same point could be made about the Lyme testing in the UK, which at beast has something like 50% sensitivity. So when you put the poor sensitivity of Lyme testing alongside the fact that positive patients are excluded from the ME sample, it would seem likely that a sizeable proportion of those with ME-like symptoms actually have Lyme.