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?