-) psychological value: eating has a great psychological value, it's pleasure (if not, you should eat better food)
-) social value: you probably won't go out with friends to have a glass of Soylent, would you?
-) Arguments about "increased productivity" because of less food preparation are ridiculous... if you can work all day long without needing a break, congratulations, you are everything common sense and science tells me is not possible. We need breaks, regularly, and why not use that to cook something. And cooking doesn't take hours a day.
-) Health: Because the supplement industry is such a thoroughly regulated and well behaving industry? If you believe that, do your research. I want to know what I am eating, and I don't when buying this mix of various powders they most likely buy in themselves. Would you give this crap to your children? Do you think we already have unlocked the key towards the perfect nutrition? (spoiler: no, we haven't, studying this is hard)
-) You can't cook: It's not hard, have you ever really tried? You don't need a Michelin star to cook solid and good food.
-) Unhappy with your current diet? Then change it, why ditch food altogether?
-) Cost, so it's not about productivity or health now, but about saving a few bucks? I doubt you save much if anything at all, it's not that expensive to buy good food, and isn't this mainly marketed towards high income people to begin with? You can afford it.
-) Soylent is revolutionary: It's not, 100% food replacements have been used in medicine for decades (just no one was crazy enough to ditch real food for it if not needed) - you can even buy it, it's far more expensive though than this, and of course I am still not for it as a food replacement for healthy adults.
-) Trust your body: Every body is different, the reason we have cravings for food is because the body tells us what it needs. This can fail us, for example when we eat too much sugar and our blood sugar levels are creating massive cravings for more down the line (I am not making a case for Coca-Cola here though), but all in all, it's an incredibly accurate and needed thermostat. If you eat more, you will ditch your blanket at night subconsciously to burn more calories by cooling down, if you eat less you will feel more cold and not do so. It's downright arrogant to think that some individual having read some studies and reports knows what is absolutely best (besides commonplace arguments like "sugar is bad", "being overweight is incredibly unhealthy", no proper doctor would ever make such bold and arrogant claims)
My opinion: This is part of a not well regulated industry, a repackaged and cleverly marketed mix of food supplements that have been available for decades, sold with incredibly high profit margins. They buy in their stuff, they mix it, prep it up with some nice fancy talk, sell it, and see dollar signs in their eyes.
Everyone should be able to do whatever he wants to as long as he is not harming others. If you think Soylent is great, then by all means, I won't stop you, I am passionate about food and am disgusted just looking at this. If someone thinks this is healthy (spare me your cherry-picked study citations), then - with all due respect - you are delusional