Because her attitude has nothing to do with it. She is a black woman speaking about racism, she has the right to be angry and sour. People don't listen unless people are angry and loud. Her "foul attitude" doesn't take away from the fact that what she is saying about Iggy and racism is right.
At the same time, you can still think that she is trash. Trashy people sometimes make completely valid points.
I sympathize with people who have a sound mind and have a classy and respectful way of getting their point across. Azealia is not one of those people,even if we might have certain opinions on racism in common.