If you ate a McDonald's said their food was nutritionally complete, and you ate it everyday for a week, and then got sick, who is to be blamed? Of course, given McD's reputation I'd say you're to be blamed. But in this case Soylent is untested, and so far doesn't even substantiate its claims very well. And even McD's doesn't go so far as saying that their food can replace your meals (or maybe they have? I do not get that vibe though), while Soylent here is supposed to do that (the vibe I got from his blogs, at least -- this is supposedly revolutionary, no?).
Although I love cooking to bits I do find Soylent interesting as a concept, but the way they've gone about doing things isn't what I'd approve of myself.
And as I see it, a majority of the arguments here do not boil down to "Much smarter people are working on this and they haven't solved it, who the hell does this KID think he is?!?" or "He's violating ALL KINDS of FDA regulations! [none of which I can name]". For the former, Soylent is simply making unsubstantiated claims, to which much smarter people have not even come up yet. If Soylent is indeed that smart, then they better have good claims to back it up. For the latter, I only saw one commenter talk about breaking FDA rules, and he was only speculating about them, and to be honest it's very likely that there's something about false advertising that they broke.
But then again the FDA probably didn't expect some company claiming that they'd come up with a food to end all foods...