It's not just gluten; it's wheat and grains in general (although I think rice and quinoa are ok in modest amounts).

There is a lot of evidence that wheat in the diet raises bad cholesterol, triglycerides, blood sugar, promotes hunger, and even has an addictive effect causing you to crave more of it. Allergies and related health problems are a whole other issue I won't discuss in this post.

Many grains also have anti-nutrient properties (something even nutritionists and registered dieticians aren't always aware of) in which some of the nutrients your body would have absorbed end up getting passed through and wasted. Phytic acid is part of the reason this happens (the wheat doesn't want animals to consume it so evolution developed a means for it to disrupt our digestive systems).

The wheat the earlier generations you speak of consumed contained FAR, far less gluten than the selectively bred and modified garbage we have today, which is one explanation for the dramatic increase in celiac disease, which cannot be explained by better awareness alone. It's also important to know that less than half of celiacs know they have the disease, and most that go undiagnosed die before 65. The stuff we have is also filled with synthetic toxins. Celiacs that follow a strict no gluten diet have lower rates of heart disease (although I admit I think this is mostly because they eat healthier overall).

The reason it's a staple of most diets, indeed for most people throughout the world, is because it's relatively easy to mass produce, and thus, easy to feed masses of people with. That says nothing at all about the health properties of it. The truth is that it's a sub optimal source of nutrition. Everything beneficial in it can be extracted more readily from foods that are more nutritious and easier on the body. We we're meant to eat primarily meat, fish, vegetables, and fruits. We did not evolve to eat grains, certainly not on the level most do.

I suspect for one that the obsession with eating grains is that it's ingrained into us (pun intended) from every angle. It's a perfect example of social influence. Everyone eats it, therefore it's strange and even treated as hostile when someone does not. Plus you really have to go out of your way and make a conscious effort not to eat any of it. The learning curve is very steep.

The recommendations made by official sources are a health disaster, and are firmly rooted back to decades old junk science from the 1950s, specifically regarding saturated fat and cholesterol. These same official sources recommend diets consisting of low fat intake, high carb intake, unhealthy vegetable oils, butter substitutes, and that grains be a major portion of our diets, which is though to be contributing to the phenomenon known as diseases of civilization.
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About organic food, the problem with our produce and meat is that even these are starved of nutrients. The soil used to grow the produce is often lacking nutrients, resulting in frutis and vegetables with little flavor or color, and the meat often comes from unhealthy animals that are fed garbage. So ideally, you want grass fed meat, wild caught fish, and locally grown produce. Organic stuff isn't much better than traditional, if at all, but it doesn't have as much pesticide residue.

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Just months ago I thought this whole gluten thing was just a fad started by a couple of snake-oil diet plans, but I really think there's some truth to it.

For anyone that's interested, I think it would be a good idea to do some research on the longest living populations of the world, such as those from Okinawa, or possibly on the lack of western-world diseases in hunter gatherer populations.