It’s more than this. It isn’t that there is only a common source. In fact, black women specifically suffer because the source is not single sourced.

To paraphrase, Black women suffer the problems of women, because they are women. They also suffer the problems blacks face because they are black. But they also face problems that only black women face. The source of problems they face as blacks and women individually may well be white men… But they also suffer the inequalities imposed on them by black men, which are different than the inequalities placed on them by white men. And they suffer the what white women impose on them that is different than what is imposed on them by black men.

The problem is that discrimination is multifaceted, and movements that only seek the liberation of one group often harbor the oppressors of another.

A simple, explicit example. J.k. Rowling is a feminist. She is also a terf. She wants the advancement of the people she deems women while simultaneously seeking the exclusion of a group she hates.

More bluntly, there are racists in the feminist movement who want to see black women suffer and those racists are not just white men.