In theory: Sexism affexts people of different classes and sexual orientations differently, eg if a poor black woman got harassed by a cop and it turned into sexual abuse, it would be difficult for her to do anything about it.  Therefore intersectional feminism is supposed to fight against all inequality in society and intersectional feminists should support other civil rights movements. Far too often in practice: Entryist nonsense where tumblrinas try to take over other civil rights groups, preventing them from doing anything not related to feminism, and/or take credit for things feminists were only tangentially involved with. Additionally, the banner is used to present non civil rights issues (fat activism) as a feminist topic.  This is why you get the hilarious "I am a demisexual voidgender foxkin" stuff - people are attempting to make personal problems political issues.  Usually the real crazy walking SJW stereotypes use the banner of intersectionalism to justify  their racism/sexism.