There is no data about long-term effects of Soylent. Everyone has only priors and nothing but priors. By the way, "domain-specific knowledge" is a prior as well.

I am not sure how are you going to gauge the proper weighting for people's opinions. This is the internet, after all. If I tell you "I'm highly credentialed. Just trust me" :-D will that satisfy you?

On a bit more serious note I prefer arguments that stand on their own, regardless of their source (and its credibility or lack thereof). In fact, nutrition is such a screwed-up field that I would probably downgrade opinions from someone who claims to be a nutritionist...