It is really possible with no problems to health to eat some kinds of meat even not cooked (this is also an old practice very common in countryside villages), the only requisition is to get the meat fresh. I agree about the non-healthy condition of a 100% meat-based diet anyhow. What about eggs and fish?
I think that a correct diet has to be balanced with the right percentages of the whole nutrients without getting it through supplements. If the totally vegan diet is the best and right way to feed the human specie, why do you need to get pills?
Finally, it is not medically demonstrated that the meat causes cancer, whilst it is well-understood that the pollutants in general increased the cancer in the industrialized cities...