Why do people want to separate american mixed people(mixed with black and white) from latinos?

if someone mistakes an african american mulatto for hispanic there is always a person figuratively breaking their neck to say that is not the case.or if an american mulatto tries to hang out with hispanics or try to get involved in a relationship with an hispanic person.there is always someone trying to stop that unity.Latin america has mulattoes(not trying to say that latin americans can only be mulatto i added this because i know someone will try to divert the point and argue that latinos are not only mulatto)but yet if a more fully looking black hangs out with hispanics there is no one trying to stop that.but there are people having a problem with it if an african american mulatto that is mistakable for a mulatto latino does it.Why do people have a personal vendetta to stop someone from getting in where they fit in?