Sugar is not bad for you. Fruit juices and sucrose in the context of adequate nutrition is good for you. Getting a fraction of your calories from sugar is a good idea.
I doubt grains are that big a deal for most people.
Unsaturated fats are the only thing in the diet that is clearly bad and people still eat loads.
Unsaturated fat (excluding trans fat) is good for you...this is one of the few things in nutrition that's entirely uncontroversial. I'm pretty sure you're thinking of saturated fat, but you're wrong about that too, since it's not "clearly bad". The fact that no one on either side of the theories around saturated fat seems capable of accepting is that the science is not yet firmly conclusive in either direction.
C.f.
http://www.scientificamerican.com/article.cfm?id=carbs-again...
"In March the American Journal of Clinical Nutrition published a meta-analysis—which combines data from several studies—that compared the reported daily food intake of nearly 350,000 people against their risk of developing cardiovascular disease over a period of five to 23 years. The analysis, overseen by Ronald M. Krauss, director of atherosclerosis research at the Children’s Hospital Oakland Research Institute, found no association between the amount of saturated fat consumed and the risk of heart disease."
I definitely mean that unsaturated fats are to be avoided. Saturated fats are quite safe, however large single sitting intakes are a bad idea because of increased endotoxin absorption. Monounsaturated fats are probably fine, but other unsaturated fats accumulate in tissues over time and cause disease. DHA is implicated in alzheimers. PUFAs, including omega-3, are tied to cancer and metabolic disorders. Even the so-called essential fatty acids are understood to interfere with the endocrine system over time.
Coconut oil and dairy fat are safe. Other fats should really be minimized. To the extent that any fatty acids are "essential" you'll easily get them incidentally from foods. All vegetable oils are bad for you and fish oils are bad for you.
Ah ok wow, my mistake. It's so common to hear people confidently (and wrongly) saying that saturated fats are DEFINITIVELY SCIENTIFICALLY PROVEN to be bad for you that I just assumed that you mistyped.
That being said, from what I can tell, unsaturated fats are a far cry from your claim of "clearly bad", and even farther from "the only thing in a diet that's clearly bad". From a quick Google search, it appears that there's preliminary evidence that high amounts of PUFAs increase the rate of metastasis in rats with cancer, and preliminary evidence that high amounts of PUFAs decreases the "all-cause mortality" rate and rate of cancer events in humans with cancer. With such a low bar for "clearly bad", one could dig up a thousand and one studies about refined carbs (let alone sugar) that make it infinitely more "clearly bad".
*I mean that in the sense of reading up on things from reliable sources (studies etc), not that I'm a researcher
I doubt grains are that big a deal for most people.
Unsaturated fats are the only thing in the diet that is clearly bad and people still eat loads.