So it is said (and, I believe, documented), and 'worse', but I don't think they were necessarily the first to have done such experiments
It would provide some 'answers' to some questions, but only in relation to 'populations', not individuals - i.e. it could produce estimates of 'averages' in the population, or of the proportion of a population that had a certain outcome etc. - but, as I've said, that is of limited usefulness in relation to an individual, witnessed by the fact that virtually the whole of the science of Statistics revolves around the fact that there is 'variation' (between individuals or whatever).
This is something which I think morqthana probably overlooked. Yes, trials or surveys could establish that, say, when groups of people were subjected to a certain electric shock, more would survive when there was RCD protection than when there was no such protection (and one could even estimate the probabilities of survival with/without RCD protection). However, going back to what I said that morq 'jumped on' (that, if someone had survived a shock which caused an RCD to operate, it would be impossible to know whether or not they would have survived in the absence of an RCD), if an individual survives a shock which causes an RCD to operate it is clearly NOT necessarily the case that they would not have survived without the RCD, even though trials may have established that 'on average' (across groups of people) more survived with RCD protection than without it.
In particular (given the marked variation between individuals) the primary reason why a person survived a shock which caused an RCD to operate may have been that they were particularly 'resilient' to electric shocks (i.e. needed a much worse shock to kill them than would kill many other people) - and it therefore could be that they were equally 'resilient' to the shock when there was no RECD protection.
As above, there is a wide degree of variation between individuals - not to mention, of course, the fact that the nature of the shock (points of contact, skin moisture level, duration etc. etc.) make big differences.
I have seen people who (often without knowing it) had hearts so electrically unstable that they were at constant risk of spontaneously developing a fatal disturbance of heart rhythm (the most common cause of 'sudden death') - so, in them, an electric shock of only 1 mA, or less, might be enough as 'the final straw'. Conversely, although I obviously can't know, I imagine that there are individuals who would/could survive an arm-to-arm shock considerably in excess of 30 mA.
I think the answer to that is essentially a no-brainer - not only morally/ethically but also because we obviously cannot 'unlearn' things.
There are many examples. For example, much/most of what we know about the biological dangers of ionising radiation derives from events and experiments which are more than a little 'ethically questionable'
Kind Regards, John