To a degree of course, just 'but it might work' would be enough I guess, the same way someone needs to at least not be told something is a placebo for a double blind study to be "valid" ("methodologically sound" would a better term I think?). I did read quite a lot on the topic and much has been written about it over the years, but this was 10+ years ago for me, I don't remember enough to really make a coherent argument that addresses the details.