Are psychological-biological group differences (between social classes, races, men and women) real with respect to... intelligence, aggression, conscientiousness, strength, height, educational attainment, work ethic &c &c...
Are they real? What does the evidence say? What does rigorous reasoning say?
I have intense personal experience of such issues - because in 2008 I was briefly at the centre of an international media firestorm in relation to differences in general intelligence between social classes, and the effect such differences would be expected to have on admissions to universities of varying levels of selectivity.
My position was quite straightforward - but it depended on assumptions which, it turned out, were not shared by the majority of people in mainstream politics, education and the mass media.
My basic assumption was that it was plausible that there would be differences in intelligence, hence IQ measurements, between social classes. This arising from the application of normal psychological standards of evidence; mainly the a combination of the high heritability of IQ on the one hand - and the causal association between IQ ranking and a wide range of life outcomes including job status, educational attainment and salary.
Given my assumption that class differences in average intelligence (and distribution of intelligence) were inevitable, for me the only live issue was how big were these differences in a given situation, and how great an effect would be expected on that specific situation.
BUT - if the solid assumption is that there are NOT class differences in intelligence - then all of the above evidence and reasoning, and any other potential evidence that might be brought-forward, must inevitably be false, for one reason or another; and the only live issue is to find the specific falsehood in each study and expose it.
And fault-location need not be done too carefully, since even if a fault could not be located, it is already known for sure that a fatal flaw is present - because the given answer was wrong.
Indeed, the main flaw intrinsic to research showing class differences in intelligence was assumed to be malicious lying in support of a right-wing/ fascist/ 'racist' political agenda - because only a person who (whether openly or secretly) hated and/ or despised the 'lower classes' would even do research into intelligence differences according to class.
In other words any and all studies claiming to show intelligence differences between social classes were either bad-science because incompetent; or, more likely, bad-science because fraudulent.
So, from this experience, I learned the futility of arguing about evidence when it comes to matters of fundamental assumptions - of metaphysics. If you assume that group differences are plasuible - there is ample, high quality of evidence consistent with such assumptions. But if you assume that there are no such differences - then it is an easy matter to explain-away any and every piece of apparent evidence, and to dismiss the arguments of those who oppose you.
The only way that resolution could be found, in principle, would be if the participants were prepared to reveal and evaluate their fundamental assumptions; to try to see which was more plausible; or indeed whether some other set of assumptions might be superior.
Metaphysical analysis and evaluation is therefore an absolute necessity for resolving this particular issue; and by extension for all similar issues in relation to group differences.
How important is this? Extremely important; because the denial of such group differences is the basis of almost all major Liberal/ Left/ Labour-Democrat party policy over the past half century - because it is by assuming that there are zero significant and relevant class/ race/ sex differences of a psych-biological type that the alternative inferences can be put down malign to class/ race/ sex prejudice - and such prejudice is the rationale for most modern Establishment policy.
But upon this metaphysical assumption of no-difference rests a vast interaction of vested interests - upon this assumption rests the entire rationale of the entire Establishment of all the major social systems (politics, civil administration, law, business, health, education, arts, police, military and the mass media, mainstream religion... everything).
Honest metaphysical analysis is the only possible answer - but such is always and at any cost avoided.
So, there is nothing to be done unless or until the discourse has been shifted to metaphysics. And meanwhile accumulating or presenting evidence and reasoning will continue to be futile; a waste of time at best and counter-productive more often than not...