An actually good answer.

But what I disagree with is that the word race being used by racists is justified to call random people racists. I do not use it personally anyway

“racism is anti-social” ?

Yes you are proving my point

As you said racism is the belief that races exist AND that they should be hierarchized. It is true that the genetic diversity is too big in the race groups for it to be biological races, so the word usually is a synonym for way too big ethnic groups.

Thus using “race” is biologically ambiguous and “ethnic groups” should be preferred, however it is still very well socially defined. Using “race” in a social context makes sense and is far from being racist.

Saying “black people are discriminated” is a talk about race not ethnic group. “Black people” is not an ethnic group, it has hundred of ethnic groups and some ethnic groups are mixed race.