That was told to be by a half japanese person who grew up in japan.

And your own link talks about discrimination:

Soon this, too, became a taboo term due to its derogatory connotations such as illegitimacy and discrimination. What were central to these labels were the emphasis on "blood impurity" and the obvious separation of the half Japanese from the majority of Japanese. Some English-speaking parents of children of mixed ethnicity use the word "double."[30] Amerasian is another term for children of mixed ancestry, especially those born to Japanese mothers and U.S. military fathers.

If anyone on reddit talked about blood purity, what would you think about them? Seeing there are hafu celebrities is like saying that there's no racism in the u.s. because there are black celebrities.