One problem I've had in speaking to others about Paleo, or even just low-carb and avoiding grains, starches, and sugars, is that people that have had success on other diets, are more body-building minded, or are firmly in the calories-in-calories-out group don't seem to listen to simple reasoning.
You can cite studies that show how insulin and blood sugar are intricately tied together and are the keys in not only fat loss, but also in most Western health related issues. Studies that show how mice on controlled diets that would normally maintain a lean frame actually become obese when insulin or other hormones that increase LPL activity on fat cells are controlled.
These people may even understand the basics behind the GI chart, and understand that higher GI foods translate to more blood sugar and thus a higher insulin response. But, getting them to relate to the fact that calories-in-calories-out isn't the most important concept, that the more traditional calorie-restriction diets actually show results because of an unconscious reduction in (bad) carbohydrates, is just not working. Body builders, or at the very least people that are more concerned about putting on muscle mass, are the worst, because they seem to be very in to the raw science of things, but make things so complex that they can't focus on the basic concepts. Occam's razor, it seems, is totally lost on them.
I myself have only really started to go back to basics, and recently reading "Why We Get Fat" has really simplified much of concepts behind a low-carb (or rather, just a no-bad-carb) diet. It's not even the Paleo part that gets to people, it's just the simple ideas of getting rid of bad carbs, which doesn't mean low carb, and not being so afraid of good and animal fats. I have only my own experiences to go on - how I'm effortlessly losing body fat, how my mood is uncharacteristically stable, and how various other things have changed positively (acne gone, heightened senses, better sleep), but they write these off as well.
I respect many of them for progress they themselves have made and the lengths they have gone to educate themselves on these concepts, but it is very frustrating to me that so many of them are so stubborn. This isn't so much a question, as it is somewhat of a way for me to vent off frustration, but how do you go about dealing with people like this? Many of them refuse to read things which disagree with years of previous research they might have done, or against progress they have made before. It is just unfortunate, I feel, that when you realize the person you're arguing with won't listen to reason, that ceasing the argument didn't feel like you've lost. I just have to focus on my results, and wish them the best of luck I suppose.