In a letter to Mexican composer/conductor Charlos Chávez, Copland wrote “I am terribly afraid of what you will say of the Salon Mexico–perhaps it is not Mexican at all and I would look so foolish,” which shows his concern regarding appropriation. He may have gone ahead with orchestrating and publishing the piece, but he was well-meaning in the same way that Dvorak was with his New World Symphony. Some differences here are that Copland interacted mostly as a tourist in Mexican culture and drew on more accurate sources for Mexican folk melodies.
In addition, Copland published The Story Behind My El Salón México in the quarterly journal Tempo. He discusses that the music he heard during his two summers in Tlaxcala, isn’t what inspired this piece as much as the spirit of Mexico, specifically regarding “their humanity, their separate shyness, their dignity and unique charm.” He, like many other composers writing in this style, relied on the use of folk melodies, but his goal was never to quote them directly, instead choosing to heighten without falsifying the natural simplicity of the songs.
On the subject of whether this was good or bad appropriation, I would argue that this was good appropriation because of his genuine approach to the piece; Copland never claimed or exploited Mexican folk traditions. Additionally he was aware of his position as a white man composing in a Mexican style (even calling himself a gringo) and was completely taken aback by the support that he received from the Orquesta Sinfónica de México (who premiered the work with Chávez in 1937). The group viewed his composition as a foreigner finding their melodies as worthy in the world of Western repertoire which gave him affirmation regarding his fear that the piece would be perceived as a foolish attempt of claiming Mexican culture.
Crist, Elizabeth B. and Wayne Shirley. The Selected Correspondence of Aaron Copland. New Haven: Yale University Press, 2006.
Copland, Aaron. “The Story Behind My El Salón México.” Tempo, no. 4 (1939): 2-4. http://www.jstor.org/stable/943608
Copland, Aaron. Letter from Aaron Copland to Carlos Chávez, October 15, 1934. Manuscript/Mixed Material. Retrieved from the Library of Congress, https://www.loc.gov/item/copland.corr0191/. (Accessed November 07, 2017.)
Schaal, Eric. Aaron Copland and Carlos Chávez. , . Photograph. Retrieved from the Library of Congress, https://www.loc.gov/item/copland.phot0014/. (Accessed November 06, 2017.)