As a health measure? The market for weight-loss shakes and other dietary solutions is saturated, and most of it appears to be complete shit. Dietary shakes are easy to come by, and are almost universally reviled because they don't work as advertised and taste disgusting.
Is Soylent a supposed to be a remedy for malnutrition? Why is drinking a bunch of vitamins a better option than taking a dietary supplement? How does Soylent account for the fact that nutrient absorption is less efficient in artificial supplements? Why not just eat quality, healthy human food?
But, far and away the worst and most appalling argument is that soylent is "convenient," and that it's beneficial to people who "don't have time to eat." I'm sorry, but if you can't find time to eat human food, the issue is your schedule, not the food. Correct me if I'm wrong, but eating is pretty fucking important. If you are in a position where feeding yourself actual sustenance is inconvenient, then there is a probably a severe deficiency with your schedule and a problem with your priorities.