In The House on Mango Street by Sandra Cisneros, protagonist and narrator Esperanza Cordero witnesses and experiences various forms of prejudice directed against her ethnicity while growing up in a working-class neighborhood in Chicago. The prejudiced behaviors of the people Esperanza encounters stem from ignorance and lack of interest in other cultures, as indicated by the quotation cited in your question.
Here are three quotes and situations from the text to consider for the theme:
Esperanza experiences prejudice as soon as her family moves into the neighborhood. In “Cathy Queen of Cats,” a girl named Cathy agrees to be her friend, but it will be a conditional friendship:
But only till next Tuesday. That’s when we move away. Got to. Then as if she forgot I just moved in, she says the neighborhood is getting bad.
Cathy claims a relationship with the French royal family and that her father will travel to France to inherit property, implying that she is Anglo and sees herself as above the residents of Mango Street that she regards as “bad.”
Cathy’s bluntness indicates a lack of respect and courtesy toward Esperanza's feelings and another culture. The ease of which Cathy makes these unkind remarks indicate the prejudices are ingrained, something taught to her by her parents.
The story “Those Who Don’t” specifically addresses the issue of racism and its basis in fear. Esperanza relates:
Those who don’t know any better come into our neighborhood scared. They think we’re dangerous. They think we will attack them with shiny knives. They are stupid people who are lost and got here by mistake.
Her description shows an awareness that she, her family, friends, and neighbors have been "othered" and reduced to cartoon figures because of stereotypes. She notes in turn that when they drive to other neighborhoods, “our knees go shakity-shake,” further indicating the mistrust between Mango Street and other neighborhoods.
In “Geraldo No Last Name,” Esperanza’s acquaintance Marin meets a young man named Geraldo at a dance. When Geraldo is later hit by a car and injured, Marin is called in by law enforcement to confirm his identity at a hospital even though she only knows his first name. Marin finds herself in an inadequately staffed emergency room, waiting for a surgeon who never arrives—two clues that indicate there isn’t much concern for the well-being of the neighborhood’s residents.
Through a passage of indirect speech, Marin’s experiences show the callous indifference and ignorance on the part of the police and hospital staff toward Geraldo and Marin as Latinxs and immigrants. Esperanza says in regards to the police and hospital staff:
What does it matter?
They never saw the kitchenettes. They never knew about the two-room flats and sleeping rooms [Geraldo] rented, the weekly money orders sent home, the currency exchange. How could they?
Esperanza’s encounters with varieties of ignorance, mistrust, and prejudice became a part of her coming of age process and inform her thoughts and aspirations of being a writer. As one of the las comadres tells her,
You will always be Mango Street. You can’t erase what you know. You can’t forget who you are.