And I'll repeat something I don't think I emphasized enough: you can't weaken ethics just for one experiment. Weakening ethics codes for experiments whose benefits outweigh the harm to others also weakens ethics for experiments of other types.
I have never argued that standards should only be weakened for one experiment. My argument here is for a whole-sale universal shift to a different standard.
First of all, it obviously was not banned already; Tuskegee did pass enough previously accepted norms of conduct for it to actually happen.
Tuskegee was a secret, as I've already said, so how did it pass norms of conduct? Secret scandals do not show anything about accepted norms of conduct, or rather, they show the opposite of what you want it to show: that they couldn't get away with it publicly and had to keep it a secret. No one went to the newspapers at the start and said 'we're going to kill a bunch of blacks with syphilis' and the newspapers printed that and everyone was 'well ok that's within accepted norms of conduct' and then later changed their minds.
Second, modern ethics codes make a much better Schelling point
Let's say that complicated arbitrary systems of 'consent' and 'benficience' which cannot be defined clearly and lead predictably to many kinds of deeply suboptimal outcomes are, in fact, a Schelling point. So? A Schelling point is not a magic wand which justifies every sort of status quo; why should one think that the violations halted by the existence of a Schelling point outweigh instances like smoking where the enforcement of medical ethics leads, by the most conservative estimates, to millions of excess deaths?
We don't use evidence from illegal searches because although using the evidence would cause more benefit than harm in the particular case we want to use it in, using such evidence has the effect of encouraging illegal searches, not all of which are going to be in similar cases.
And which encourage overbearing tyrannies which themselves cause massive death and disutility. Here's an example of where the slippery slope bottoms out at something bad. But what is there for principles like randomized trials as the default?
breaking the code has the effect of encouraging more breaking of the code, not all of which will be in smiliar cases.
What are these huge, well-established, overriding threats? Who is the Stalin or Mao of randomized trials?
A look at all natural foods through the lenses of Bayesianism, optimisation, and friendly utility functions.
How should we consider foods that claim to be "all natural"? Or, since that claim is a cheap signal, foods that have few ingredients, all of them easy to recognise and all "natural"? Or "GM free"?
From the logical point of view, the case is clear: valuing these foods is nothing more that the appeal to nature fallacy. Natural products include many pernicious things (such as tobacco, hemlock, belladonna, countless parasites, etc...). And the difference between natural and not-natural isn't obvious: synthetic vitamin C is identical to the "natural" molecule, and gene modifications are just advanced forms of selective breeding.
But we're not just logicians, we're Bayesians. So let's make a few prior assumptions:
Now let's see the food industry as optimising along a few axis:
The last point is the weakest one, though. Long term health impacts are fiendishly hard to measure (by anyone), and consumers' memories are short. The main things that the food industry wants to avoid are blaring headlines like "salmon saturated with mercury", "sugar linked to cancer", or "food industry coverup". Even there, journalists can create scandals out of very little (or ignore major ones if something more juicy comes along), so the pressure to actually prioritise long term consumer health is very weak. So most optimisation pressure is along the first two axis.
So the food industry will strongly push to decrease cost and increase satisfaction, while mostly taking a random walk on long term consumer health. Given the assumptions above, this means that we'd expect the long term health impacts to worsen (because there are far more negative products than good one). This somewhat similar to the importance of programming everything of value into a friendly AI, lest the things not programmed get squeezed out.
Now, what does "all natural" mean in this setting? It means that the natural food industry is facing a massively constrained optimisation problem. They are extremely limited in what they can do (compared with the rest of the industry), and it mostly involves shuffling around with products we suspect to be benign or positive. Similarly with GM modifications: selective breeding is much slower and uncertain, so the optimisation pressure is less: they literally can't change things as much or as fast. One supporting argument for this is that all natural or GM-free products tend to be more expensive or less satisfying than others, demonstrating less optimisation pressure.
This is entirely not a result I expected to find. Pushing it to the extreme, it would seem that the most traditional and unchanged food (after removing stuff we know to be bad) is likely to be best, as long as people don't get too inventive with them.