This guy is either a complete bullshitter or highly delusional. My guess is a little of both.
He suffers from a recently-discovered condition (see other threads) called Medically Unexplained Psychologising (MUP), also known as Wessely's Disease. In other words, he's a muppet.
Great work getting a reply from him though, and good on him for that I suppose; it opens the possibility that we could open a real dialogue with him and confront him with the evidence. Probably best if we do so with one voice rather than bombarding him with abuse, otherwise he'll just clam up. Let's get our best advocates on the case and continue the conversation.
The most startling part for me is that he claims not to understand how they made the leap from prostate cancer to CFS. They've explained this in a perfectly clear way, thus:
They read the prostate cancer/XMRV study and noticed that it involved an association with deficiencies in the RNASEL pathway. They recalled that several studies have found an association with RNASEL deficiencies and CFS. They put all that together and postulated that XMRV may be linked to CFS. They then tested and found that, lo and behold, it was!
In other words, they made that leap based on scientific evidence. The fact that their theory proved dramatically correct is yet further evidence that they are on to something. (Even though they did also find XMRV in CFS patients without RNASEL deficiencies). The fact that their theory was based on a logical connection in the first place doesn't count as scientific evidence to the wider world, but to me such chains of reasoning DO count as scientific evidence, if only to the individuals who constructed those chains. After all, they have constructed a theory, tested it, and found it was correct. What does the scientific method mean if not that?
It might well be worth explaining the above to him, perhaps look up the RNASEL details and WPI quotes first though and explain it a bit better than I have done above.
Finally, to be fair to him, I do think he's right that it's too early to be trying treatments with antiretrovirals, which might have nasty side-effects further down the line. It's more appropriate to wait a bit for more reliable treatments, IMO, there will probably be lots of options including natural ones that are much safer.