The ‘black community’, ‘Irish community’, ‘catholic community’. And those do often work - frankly, it’s often the only thing that works when that community does have some specific interest.
It’s for lobbying and other pressure tactics, yes?
Civil rights is a specific example of a universal interest: equality before the law. The rise of the Nazi party is an example of people forsaking their own interests for a facade of collective interest that covered over the personal interest of a few leaders - Nazi Germany was extraordinarily corrupt, and of course ruined the lives of and killed most of the people who it claimed to exist for the interest of.
It is interesting that you bring up "Catholic interests," because the Church is naturally opposed to concepts like "Irish interests." The Church doesn't want its members to divide themselves along ethnic or other lines because that would detract from their Catholicism. It is no accident that the Nazis - the most famous example of an "ethnic interest group" - had to destroy or subsume every other kind of organization to exist.
If you were an Irish immigrant in NYC in the 30’s, would you still say that about an Irish community group?
How about a Latino workers group in 70’s Los Angeles?
Or for that matter a ‘black community’ group in 70’s Los Angeles too.
LA has always had a lot of gang warfare, which divides itself along ethnic lines because that's the underbelly of human nature. Gang warfare is a great example of everybody doing things that are very bad for themselves and others because of a perceived division with little basis in fact. If there's enough gang warfare I guess you could see racially segregated unions, like in the deep south, but that is again against worker's interests just like how segregated churches oppose God.
It is very difficult to find even a selfish motive for segregation unless you are an actual slaveowner or apartheid government official.