I think there's a simpler explanation--one completely overlooked by the authors. Many people are skeptical that the intended effects of government programs seeking to produce equality will be the actual effects. Is racially gerrymandering college admissions or small business loans or vaccine distribution going to produce non-zero sum gains that accrue to everyone? Who knows.

The results in the study can be explained by:

1) Nearly everyone, whether in the minority or the majority, believing that the majority will be harmed; and

2) People in the majority rationally opposing those policies based on that premise and people in the minority rationally supporting those policies based on that premise.