The debate is indeed odd. Nobody would seriously argue that skin color is attached to social behaviors; its a minor genetic variable that's not accociated with anything.
Therefore, if mass killings in the US are primarily perpetrated by white people, the logically one has to look for any social conditions which incline them to commit said crimes........or enter into a discusison about mental health (which takes you back to the aforementioned social conditions.)
Mental health problems are, one would assume, rather evenly distributed. This snippet from psychiatry.org would seem to back that up:
Rates of mental illnesses in African Americans are similar with those of the general population. However, disparities exist in regard to mental health care services.
...as well as point out the extenuating factor, that mental health services are not available to the un and underinsured, an issue which affects Black Americans more often than White.
Yet, when faced with the stressors of life, for some reason, mentally ill whites far more often than mentally ill blacks seem to believe that mass murder will assuage their pain.
Not having a background in mental health science, I can't imagine what the reason for this might be. But I'd love to hear a discussion about it ---- rather than ignoring it, as the politicians seem wont to do.