I largely agree that "nutrition science" does not have rigorous standards. One of the reasons for this is that it's very hard to test hypotheses, legally, on people. And there's an over reliance on self reporting.
Now, I personally find your tolerance for what would be considered unsafe way too low. High doses of mercury will kill you very quickly. Low doses of many things, legal things, will kill you slowly.
As for "kill you slowly" things, there's slowly and there's "so slow that you may as well ignore it". Cigarettes and asbestos belong to the former group and guess what, they're controlled and people know about the dangers. Dietary stuff sits squarely in the latter - most of the "causes cancer" stuff won't have any noticeable effect on you in few decades, and if you eventually die of cancer it still won't be clearly connected to a particular lifestyle choice.
It's basically paranoia coupled with inability to multiply probabilities (or knowing one should do so).
And for the lay person I agree.
The problem is that it isn't black (poison, electric shock) and white (broccoli).
For the sake of the gray argument let's ignore e-coli and smoking. A good example here is consumption of sugar. It's not regulated because it's not poison in the short term.
So saying that it's okay to eat as much as you like because the CDC does not consider it poison is probably not the right way to go.
Now picking between a Paleo or a Vegan diet. I think we can agree...
I didn't mean that. That would be going to absurdity in the other direction. We know that "sugar is bad for you in the semi-long run" as well as "breaks teeth in the short run", so there's a reason to limit it. As you say, this isn't black and white.
> And a very strong underpinning for your stance is that the origin of cancer, for instance, is yet to be found.
I don't think origin of cancer will be in any way directly related to the food we eat; it would be like saying that the reason a tyre is flat is because of a nail factory in China. The underpinning of my stance is basically pure pragmatism - if something commonly used would actually give you cancer, it would be already controlled or banned altogether. The effects most of those overblown "X contributes to cancer" papers talk about are so small that you can absolutely ignore it, because the probability of getting cancer from described X is smaller than getting hit by a car driven by the researcher who wrote the paper, who was distracted by the news about a lottery he just won.
People need to learn to ignore stuff that's so unlikely that it's insignificant. It's funny, because the definition of "insignificant danger" is pretty much "so unlikely that you can ignore it".
I listen to absolutely nothing of what comes out of the field of nutrition science. I am aware that this may make me some number of shades less healthy, but the savings in time is well-worth it.
I consider all nutrition studies to not be science, in the same way that I consider a kid pulling ants apart with tweezers to be not science. The information gleaned is of no practical value. What little there is that is of worth ends up getting baked into laws and regulation, so again, I don't have to worry about it. (e.g. mercury is bad for you.)
I may be interested in somebody's self-experimentation results. Tim Ferriss wrote about the slow-carb diet, I gave it a shot, and lost weight with it. I similarly lost weight with the intermittent fasting diet. Do I care about the relative health effects vs. the so-called Standard American Diet? No. All I can see, all I care about is whether it makes me lose my excess fat.
The human body is too complex for any nutrition study to approach a causative standard of rigor. It's impossible to control for all the variables.