> EDIT: There's a reason Soylent is vegan; not to appease animal lovers, but because its healthier for you.
More likely, it's because it's easier to utilize without spoilage.
Also, the cancers you refer to are not specific to meat, they're specific to cooked (moreso charred) food.
Milk and eggs provide a complete protein that's hard to find elsewhere without doing a lot of pairing.
That said, the "emaciated" point is probably moreso about the "low fat" part of the comment. Fat is critical for hormone production among other things, and it would be very hard to be a "powerlifter deadlifting hundreds of lbs" without adequate fat intake. More importantly, saturated fat (and specifically dietary cholesterol, the kind found only in meat and dairy) is particularly well utilized for hormone production.
http://www.ncbi.nlm.nih.gov/pubmed/6538617