While people who make silly, unevidenced arguments for veganism (that eating animal flesh means absorbing the distressed vibrational energies of slaughtered animals or some stupid crap like that) are definitely the minority. The only popular current author/speaker I can think of pushing that kind of stuff is Will Tuttle, and I don't personally know anybody in the vegan community who doesn't laugh at him, though presumably somebody buys his books and attends his speaking engagements. :shrug:
A better source of diet woo would be raw foodists. Oh my lack of god, their enzyme worship and focus on "living foods" is strange in the extreme, and generally not even supported by common sense, let alone evidence. Also, their food tastes horrible. I was given some "raw chocolate" which hadn't been tempered (since that would require heating it above 110 degrees or whatever the magic number is) and was thus too bitter to be overcome by the agave nectar used to sweeten it. I actually threw away a hunk of chocolate the size of my hand. I mistrust people who can make even chocolate taste bad.
The Weston A. Price people are also a great source of diet woo. Apparently high serum cholesterol is good for you. People also need to eat more organ meats. Oh, and raw milk is totally safe, even for babies- their rationale for why it's illegal in many places moves into conspiratorial directions. My favorite though is the meat-based infant formula (seriously, it was various organ meats thrown in a blender and made into a slurry) I found on their website once.
http://www.westonaprice.org/children/recipes.html :scared: There's one of them in action in the health forum.