While I totally get what you mean, I’d guess for scientists, the answer is generally, “no”. Expected outcomes for trials like this are a whole lot less certain

While I totally get what you mean, I’d guess for scientists, the answer is generally, “no”. Expected outcomes for trials like this are a whole lot less certain to the people doing the work, that than it seems on the outside, so i think it wouldn’t even occur to the scientists that the downside of “withholding” treatment from the tiny (relative to the population) control group comes close to the upside.