I sympathize with the position you're taking, their marketing is certainly pursuing the busy-body yuppie audience. I think if you spend some time reading comments and posts from users of Soylent online you'll see a lot of people are buying it because it is inexpensive and nutritious, while still requiring very little time to prepare. I acknowledge that, as an example, a healthy and cheap meal can be made from beans, rice, and frozen vegetables, but it takes non-trivial energy to make that every day, which is hard to find on a consistent basis after working or studying all day.

I certainly see Soylent as a means to improve public health and the state of mass food production. I think if you take an honest look at Rhinehart's blog posts about Soylent and his other (somewhat radical) personal experiments you'll find that his pursuits are similarly aligned.