While I am definitely not an "ends justifying the means" kind of guy, there is a certain point at which, even if the methodology is unethical, factual findings have their own merit.
If, for instance, the early studies that determined the existence and force of gravity were all done- and replicated- with human
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...and were never repeated in any other way, researchers who went forward from that point using that data but behaving in a way we would not find reprehensible might be criticized for not replicating the results of the earlier experiments with inanimate objects.
But they could assert the defense that the data gathered- unethical though we deem the earlier methods- was valid, and the only thing gained by repeating the experiments ethically is some vague moral high ground.