You're right, of course, that there is evidence from experience, and other comments discuss the extrapolation of such evidence to Soylent, both for and against its risk to health.

I mean rather to address the calls for randomized, controlled experiments. Indeed, I would like to see a rigorous clinical study of Soylent, and I would not believe any specific claim about the health benefits of Soylent without at least that much evidence.

But the standard employed by most people for making dietary changes, even major ones (e.g., any fad diet), is basically whim and fancy, and perhaps that is not unreasonable given the low cost of making these changes and the difficulty of obtaining clear scientific results about diet (exacerbated by large interpersonal variation).