There's another thing people forget, too: you're made to chew things. Chewing helps break down food for digestion, and probably more importantly generates saliva, which is also very important for initial digestion as well as oral health.
Not to mention the gut is a muscle, and muscles need exercise. Eating liquid food is probably not good in the long run for your digestive system and probably causes other problems that will be evident 5-10 years down the line or more. People were not meant to eat liquid supplement.
If this is the only problem maybe it has a solution too? It shouldn't be too hard to make a nutrient-poor spongy substrate to carry Soylent.
Or, you know, just spit into the soylent as you're constituting it?