Why single out racism?
At a global level, this would not necessarily make sense (for instance, the oppression of women is fundamental to poverty and lack of development in many areas), but in the USA, racism stands out. The two worst crises of the UUA (late 1960’s and now) were both related to race. Racism in the US stems from chattel slavery, where people were uniquely legally treated as property that could be inherited, for something (skin color) they had no control over.
The UUA has done well with women becoming ministers and leaders (the 7 Principles themselves came out of the Women’s Movement within UUism).
The LGBTQIA+ community is well represented as members, ministers, RE staff, and other leadership in individual congregations and the UUA, and the Welcoming Congregation program has been very effective (we could use something similar for racism); we have also made good progress with people who are differently abled.
The UUA, the US, and the world also have a lot of problems deeply based in economic class oppression (as MLK realized, in addition to militarism and materialism); this Principle includes that, but is not highlighting it.