What confuses me about the negativity is, what's so bad about the current situation? The earliest of adopters will serve as a giant trial, and if there are problems they'll come up there.
No, they won't. Or, if they are interpretable as a trial, it'll be as the worst epidemiological survey ever run - no blinding, no followup, response bias out the wazoo, attrition, expectancy and Hawthorne effects already built in etc etc. You name a bias, this ('hand out goodies and hope someone will report problems') will have it. You ever wonder why we have things like 'evidence-based medicine'? It's because when we hand out goodies and hope people will tell us how well it works, we get people grinding up tiger penises because nothing works better for fixing your virility problems! Everyone says so! And how could they be wrong, right?
To quote myself again from my G+ thread:
For [How many people will get sick/die?], there's no way to tell. People get sick and die all the time. No one will be reporting systematically, which means that no matter how many datapoints you collect, your results will still be worthless because increased sample size only reduces random error, it doesn't reduce systematic error which sets a floor on your result's quality (see the 'emperor of China' bit in http://www.gwern.net/DNB%20FAQ#flaws-in-mainstream-science-and-psychology ) - and with a random release to enthusiasts like this, the systematic error/bias is going to be huge.
What do you expect will happen? Do you think lots of people are going to get very sick by going on a Soylent-only diet immediately, not monitoring their health closely, and ending up with serious nutritional deficiencies? That's one of the more negative scenario, but I honestly don't know how likely that is. I think people are likely to do at least one of three things:
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.