Credentials can certainly be a good guideline, but as I'm sure you know HIV- and AIDS-researchers don't make the argument that their claims are true because of

Credentials can certainly be a good guideline, but as I'm sure you know HIV- and AIDS-researchers don't make the argument that their claims are true because of their authority status (which would be an appeal to authority), but because of the research their claims are based upon - as opposed to Jenny McCarthy et al.