I never thought this preference was questionable. Family = blood relation. Thus the preference for family members makes sense because it is basic human biology. There are biological and evolutionary advantages to choosing your family members over others. And I’m not talking about nepotism in business or politics, just instances of regular everyday life like you mentioned. I didn’t hear a good reason why family members shouldn’t show more care and spend more money on people who are blood relations than those people who are not. Parents usually if not always have more invested in their own children than in other children who are not familial relations. (Adopted children also count as familial relations in this case.)

You also spoke about equality and wealth distribution. I think you’re saying that there should be no familyism in order to make people more equal to one another. For example, if a wealthy man dies, his wealth should be distributed into the commons to help the common good instead of going to his biological children. But what incentive does the wealthy man have to keep his fortune for future generations of his family if he has not control over where it ends up after his death? In addition wealth distribution can and also does occur outside of the family unit.

I also disagree with your premise that familyism is as violative as racism. In your scenario, comparing a conversation with a white supremacist to a mother buying a bike, a mere toy, for a neighboring child trivializes the issue of racism.