Sorry - such a sweeping statement as "we are not designed to eat meat" cannot be made truthfully.
Humans are true omnivores, and there has been extensive research carried out into the dietary habits of pre-historic humans, with many and varied findings. However they are all consistent in one key aspect - our very early forebears ate whatever they could get their hands on and mouths around - it was a question of survival for long enough to reproduce and raise their young so that they in turn could reproduce and perpetuate the species. Early humans ate meat - whether opportunistically stumbled upon (i.e. killed by a predator or died of natural causes and not yet gone putrid), or hunted/gathered and whether it be birds, reptiles, insects, or mammalian species. That's why prehistoric cave sites and middens are full of animal bones - the bones were not put there just to confuse our scientists, they are there because they are the leftovers from what was being eaten!
Nearly everything we eat today has been selectively bred by man over thousands of years to become what we call "fruit", "vegetables", "nuts", "grains" etc. None of our present day foodstuffs (apart from meat, fish, and eggs) even remotely resemble their early predecessors. As far as meat goes, it is still basically the same as it was eons ago, it's just that the animals it comes from have changed as man has selectively bred species for certain characteristics and to produce more meat per animal.
There is also no way our very early ancestors would have passed up the chance to raid a bird's nest for eggs - a valuable source of protein and fats for early humans. The grains that are so readily consumed today didn't exist when our very early ancestors were trying to survive - again they are the product of human intervention and development which occurred after humans started to live in small settlements.
Dairy is a slightly different matter - although humans have been consuming dairy products for thousands of years, much of it was from goats or camels and far less from cows (and there is some rather limited but interesting research about consumption of camel's milk having positive effects in auto-immune diseases, Type 1 diabetes, and autism).
There is quite extensive criticism floating around about "Paleo" type diets, including that they are not truly reflective of what our ancient ancestors did eat. The article on this link provides some interesting discussion on "Paleo", and the second link has discussion about foraging theories which would have affected how our ancestors found the food they ate.http://www.scientificamerican.com/artic ... eally-eat/http://www.science20.com/the_conversati ... ind-153290
As I have had some of my previous posts misconstrued by some readers, I would like to make it clear that none of the above is intended as criticism of either OMS or any other dietary approach to whatever disease you want to think of. MS is a "modern" disease, as are many others, and there is no doubt that diet is a major contributor, but let's be wary about making sweeping statements which are not accurate in any way.