Here's mine, specifically in the more broad sense of paleo, specifically, being grain free. This is a consideration of all four points:
Grains are scorned for these reasons: gluten, antinutrients, carbs, & low nutrient density.
1) Most varieties of grains and grain-like seeds in existence are gluten free. It's just the handful that we've picked out and hybridized to death and grown on an appalling scale that typically have gluten.
2) Antinutrients are largely neutralized through "proper preparation." In addition, most nuts and seeds, allowed in the most basic paleo guidelines, are far more dense in antinutrients than any grain, and people are not widely encouraged to "properly prepare" those. A bread made with white rice flour might seem pretty inoccuous, antinutrient-wise, compared to a bread made with ground, raw almonds and then baked at a heat that might damage oils. Some, like Sisson, say that it's an issue of context, and SADers are more likely downing large portions of grain at every meal, versus someone who snacks on a small handful of nuts here or there, and in that small amount, the antinutrients are unlikely to amount to much. But you don't hear that same "contextual exception" for eating a small amount of gluten-free grain.
3) Whether you're in the "safe starch" camp or not, there exists a solid belief in the paleo community that some starch consumption is generally safe, and often beneficial, for those with healthy metabolisms. With this in mind, how is 50 g of carbs from soaked, sprouted buckwheat any different than 50 g carbs from a peeled, white potato?
4) Grains are low in nutrients, true, but if white rice is DEVOID of nutrients and is considered acceptable by many, why not a bit of soaked quinoa instead? Compared ounce for ounce, cooked quinoa and teff are more nutrient-dense, marginally, than a cooked potato (white OR sweet, beta carotene aside). Cooked buckwheat runs about on par with potatoes for overall nutrient density. Sure, peeled potatoes and soaked grains will never be as nutritious as eggs or meat, even conventional forms, but I don't understand why we hate on the occasional consumption of a grain versus the occasional consumption of tubers, at least on a dogmatic level, considering the inconsistencies above.
Personally: I don't eat many grains because potatoes taste better, and I don't eat as many carbs as I used to, because I feel better when I'm not riding the blood sugar roller coaster. But the arguments don't add up to me to make me feel bad about eating nixtamalized maize in my Mexican food. My metabolism is resilient enough and my immune system doesn't think twice about it, so I count it as a starch and move on. I believe many people have good reasons to avoid grains (just like some people have good reasons to avoid eggs, shellfish, tree nuts, etc.), but I don't believe it's necessary or beneficial to make the avoidance of grains gospel.