My immediate reaction to this proposal was a feeling of being personally attacked. "Fine, meat's expensive and a pain to cook anyway, but I'll be damned if you take away my French fries too." It also seems that every fad diet, including crazy stuff like juice cleansing, promises increased "energy" and the like; in this context, the anecdotal claims are not persuasive.

Conclusion: could work on people who don't get much pleasure out of food to begin with, but associating with animal rights activism seems likely to be counterproductive. It might also be less irritating if these foods were promoted as, well, foods, rather than the only thing you will ever eat again. I could definitely see a version of Soylent replacing my standard breakfast of instant ramen if the cost were anywhere near competitive.