According to some of the science that I've read, animals will seek out the right level of protein, and it's the other macronutrients that change.
Essentially, the grams of protein that one needs to be healthy stays constant. BUT the percentage of dietary calories that the protein may be will fluctuate based on how many calories one is eating.
So, for example, if I take hte general calculation of 1 g per lb lean body mass, I need 104g a day. It's not hard to get this as a vegan -- if you are eating your nuts, seeds, beans, grains, and of course veg. Honestly, it's not. :) But, in order to get that number, I have to eat *a lot more volume* and therefore *a lot more calories* from the food to get it.
On my vegan diet, I was usually consuming about 2000-2200 calories per day. 416 of those calories were my g of protein. That's only 19% on the 2200 days.
On my paleo diet, 416 cals is 27.3% of my daily intake (average 1500 cals). It's because it's an easier-to-get 104 grams because it comes from eggs and meat. Then the rest of my food can be fat or carbohydrates. I'm currently getting about 100g from carbohydrate -- so that's another 26.7% of the diet from carbs, then 46% from fats.
I will note, btw, that when I went paleo, I decided to try the .8 g per lb lean body mass, and I was getting dizzy, etc. Overall, I was eating more calories than now (closer to 1800-2000), but my carbohydrate was about the same and fat was up a bit. When I adjusted to the 1 g per lean lb, then the problems I was having went away very quickly.
For DH, the problem that *he* was having was due to not having enough carbohydrate. He had dropped down to the 125 range, and after workouts he felt both brain fog and what he called "zombie legs" (weak in the legs). He added in more carbohydrate, and that problem was solved. On his heavy lifting days, he's likely to head upwards of 250g/day of carbohydrate with no real problems. And, he is eating fewer calories than before paleo, but. . . yeah. Anyway that's complex.
That's my experience of it anyway.
People who eat all chocolate diets could be at risk of protein deficiency. Chocolate only contains about 2% protein. Other than that it's not exactly a realistic scenario. There's nothing essential in meat that can't be found elsewhere.
I haven't read the whole thread, my apologies, but you could be a primal vegetarian if you ate eggs and potatoes as your main protein sources. You can also combine sources to get a "complete" protein profile. I love meat, but for those that don't there are healthy althernatives.
I think the biggest benefits from the paleo/primal lifestyle come from NOT eating shit, first and foremost.