Or all the knowledge happily taken and used from Mendelesque cruel inhuman 'research' done in concentration camps. AFAIK no researcher was morally above and simply refused to work with those data.
So I've had cause to research this one in the past.
"All the knowledge"--most of the Nazi concentration camp research was absolute garbage. Turns out junk-science sadists create junk-science results and it is generally accepted that the overwhelming bulk Nazi concentration camp research was useless or near-useless as actual scientific research. I am unaware of any value being derived from the Josef Mengele work that you seem to be referring to--Gregor MenDel died sixty years before World War II, but please correct me if you're referring to someone else.
Some research from the Nazi concentration camp experiments is occasionally referred to, low-pressure/high-altitude research out of Dachau being arguably, as I understand it, the most valuable. (The other common cite, Rascher's freezing tests, were on nonrepresentative subjects and indicate that the moderate freezing that is safely and ethically studied is amplified, but does not step change, when freezing becomes extreme.) Where this data is used, it does not generally form the main body of research and mostly confirms what is known from other sources.
"Happily"--in the (rare) cases where Nazi findings are used, it's used with reluctance. There are evolving and hardening ethical codes around the use of this data as well, particularly from the 1980s onward; today, the use of any of this data must be explicitly detailed and the method of its collection is universally condemned.
Most troublingly for the pursuit of truth and some kind of decency, this argument typically is used as an ahistorical tu quoque, as is being done in this case. It's not a particularly good argument, though--even were it more than if-you-squint-and-pick-and-choose true.
Do you have any examples of papers which source such data? I'm curious to read the justification of it.