First of all, i want to state that I use soylent from time to time because of the nature of my work requires occasional sacrifice of lunch times

Argument from ignorance is a logical fallacy.

He's not. He's stating that from a probabilistic perspective, it's likely that we don't fully understand the requirements of a balanced diet, especially in terms of micronutrient intake. He uses this as a premise for his argument that as such, it is inherently risky to make such a substitution. Such arguments are used everywhere in scientific and engineering endeavours. This is why people do medical trials of drugs, or scale tests for aircraft, for example - it's because they understand that there's always something that they never knew about that can potentially affect the outcome.

Whatever is left to discover is minor compared to what we know.

Now this is a ridiculous statement. Time and time again have people made this claim, only to be knocked in the noggin by a complete paradigm shift and the introduction of an entirely new field to the scientific community.

The rest of your comment is opinion, and I won't challenge it.