You're assuming your own conclusion (that grains in and of themselves are not the problem, and therefore you're looking at grains as benign, albeit less nutrient-dense foods than veggies and whatnot).
That sidesteps the whole issue Paleo people have with grains. Nutrition isn't just about meeting nutrient requirements in the positive sense. The whole beef Paleo people have with grains are the antinutritive effects of lectins, gluten, phytates, and so forth--consuming more veggies or other nutrient dense food does not simply "undo" the effects of these antinutrients. It is these characteristics (coupled with, yes, the relatively lower micronutrient content) that separate grains from other carb sources for Paleo people.
Like I said before, people have different tolerances for grains (though I would suspect problems can develop over time even in people who have no apparent ill effects from their grain consumption, but that's a separate discussion). If you handle grains well, fine, no one is forcing you to eat Paleo. But there are obviously a lot of people who don't handle grains well, and Paleo provides these people with both understanding of why and gives an alternative approach. I think that's at least very interesting, perhaps commendable...certainly not something that warrants vilification.