But if you DO believe that some level of consumer protection beyond honest labelling is appropriate, then I think I can make a case that a product like Soylent should be regulated a little more than other foodstuffs. Please see the other threads of this discussion if you'd like to pursue that idea further.
The mainstream US diet and lifestyle causes unbelievable health problems: obesity, heart disease, liver damage, dental caries, gastrointestinal conditions, some chronic anxiety, skin conditions, possibly some kinds of dementia, osteoporosis, seasonal affective disorder, and on and on..
Modern governments come absolutely nowhere close to teaching people to eat a balanced diet of healthy foods or setting policy to discourage unhealthy foods. Indeed, often official policy does just the opposite.
Compared to soda, fruit juice, beer, cookies, donuts, chips, breakfast cereal, instant noodles, packaged dinners, etc. etc., a few people having temporary digestive problems for a few days before discontinuing their liquid meal-replacement diet because they turned out to have an algae allergy is really the least of our problems.
The main thing our food safety institutions do is prevent disease outbreaks and dangerous food contamination. They aren’t set up to have a meaningful effect on people’s overall diet.
The people you are talking about never heard about Soylent, and probably won't ever buy an expensive (?), bland tasting product that sounds like something from Star-Trek.
If the FDA were reorganized to significantly reduce the amount of soda, cookies, chips, and candy people ate, that would have a much more useful effect.