Vegans, I think.
Since going primal I've done a lot of reading about it and there's always a blog here or there in my research that absolutely hates the primal blueprint and paleo lifestyle. I find they're often raw vegan, or vegan. Most every other blog that scrutinizes the diet usually agrees with most things promoted in it but no one seems to want to stand behind cutting grains from the diet and some people still maintain that saturated fat in excess is bad.
The only thing I could see being considered unhealthy, from a CW perspective, is that people think grains are the only way to get fiber and that saturated fat is going to kill you.
I mean, vegans already believe meat is bad for you. Of course they'd tear the primal diet apart, claiming it's a death sentence.
I've lived as a vegan, lived on junk food, lived on a mix of junk and healthy food...I honestly have to say the best way to eat has to be eating things that are as natural as possible. I even believe someone can enjoy good health while eating grains, if grains don't mess with their gut. I do believe I am better off without them.
I highly doubt that we, human beings, would be required to select only the leanest meat, peel the skin off and just toss the rest.
I don't want to start an argument though. These are just observations I've been making during my search. When I was vegan I found plenty of anti-vegan sites. I think whenever you change your diet drastically from what is considered normal people are going to either really agree or really disagree, and people who disagree tend to disagree with vigor.