racism has its roots in extra-tribal interactions
It seems more historically accurate to say that racism has its roots in inter-tribal interactions: for instance the interactions in pre-modern Europe between Christians and {Jews, Gypsies, Moors}; the interactions in America between whites and {Native Americans, Blacks, newer white immigrants, nonwhite immigrants}; the interactions in Malaysia between Malays and {Chinese, Indians}; and so on. In each case, there is not merely a single “tribe” and its outsiders, but rather multiple “tribes” each with its own culture.
“Scary competitors” seems to be an unnecessary assumption, given cognitive biases. The coupling of fundamental attribution error + outgroup homogeneity bias + negativity bias + loads and loads of the availability heuristic, would lead people in groups to conclude that any negative (or merely confusing) experiences with other groups are representative of fundamental negative facts about those other groups.
Depending on the details, many people may even reject “quick fixes that look like treatment” to death and disease.
See for instance the conservative response to the HPV vaccine Gardasil, which prevents the most common strains of the virus that causes genital warts—and thereby drastically reduces the risk of cervical cancer. By providing a “quick fix” to protect sexually active women from a deadly disease, Gardasil reduces the “punishments” available for an action (or “lifestyle”) disapproved by conservatives; therefore, they reject it.