I’m still not seeing it. There is nothing wrong or improper with belonging to an organization whose intent it is to advocate for a certain segment of society, especially when that segment faces challenges that are specific to it and has been historically under-served. If the membership in the organization excluded people on the basis of ethnicity it would be an issue. It doesn’t; it isn’t.
You would be favoring one group over others, which fails on the criteria of impartiality. Which by definition is impartial.