What got me thinking about this was a photo that Norman Lebrecht put up on his blog of the Ukrainian pianist Natacha Kudritskaya:
She is playing in Maidan Square in Kiev as part of the protests against the government. This piano has been there for a while and quite a number of people have played on it, often with their identities concealed. Here is a clip of someone--who we can't see, but it might be Kudritskaya--playing on another occasion:
The music is Nuvole Bianche by Ludovico Einaudi, a student of Luciano Berio who moved into composing movie soundtracks and a minimalist style of composition. The pianist Natacha Kudritskaya is also a fine interpreter of Rameau. Here is a gavotte with six doubles:
Why am I bringing all this up? Because of the slipperyness of music's ideological connections. The Einaudi piece I'm sure is quite suitable for playing in Maidan Square as it would be inspiring to the protesters. But so would the Rameau, probably. Both give a comforting accompaniment to whatever you are doing, and neither has a firm ideological content. You might point out, as I have on occasion, that there is certainly an ideological context to the music of Rameau: it was written very much to gild the Bourbon lily and the French aristocracy of the ancien régime. But, like most instrumental music, the ideology comes from the context, not from any actual content. A triad or a scale has no ideology, that comes from the surrounding circumstances. Played for the amusement of the roi in his chambers it honors and supports the aristocracy. Played to entertain or comfort the protesters in a square in Kiev, it has an entirely different purpose and ideology.
This is why a composer like Dmitri Shostakovich could be called a dissident (probably wrongly) by some even though he was awarded many prizes by the Soviet Union (including the Order of Lenin and the Stalin Prize in the arts) for his patriotic work. He wrote pieces that were obvious examples of socialist realism, and others that have been claimed to be sardonically undermining the regime. He could get away with this because the music, instrumental music without words, is without ideological content. Now, true, it is possible to write "codes" into instrumental music and Shostakovich did that. He put the letters of his name (and the name of a love interest) in his Tenth Symphony (and other places), but that is something that has to be uncovered and pointed out. And besides, that is not the kind of thing that gets you sent to Siberia. You can claim, perhaps with some justification, that the emotional power of his Symphony No. 5 offers comfort and support to the long-suffering people of the Soviet Union, which it certainly does. But it does not do so in an overtly ideological way, by opposing the regime. Which is why, though he was denounced from time to time, he was never arrested.
Another example might be Carl Orff. His cantata Carmina Burana, premiered in Frankfurt in 1937, was hugely popular in Nazi Germany and he also was commissioned to write music for A Midsummers Night's Dream after Mendelssohn's music was banned because he was a Jew. Whether or not Orff was himself a Nazi is irrelevant: during the Nazi era, his music was deemed to be ideologically suitable for the regime. But now these associations are forgotten and the music has a niche in popular culture exemplified by its use in countless contexts (from The Simpsons to The Matrix), some of which can be seen here.
The only music that has an indisputable content is music with words and even then the meaning of the words might be ambiguous--what did the words of O Fortuna mean in Nazi Germany?--or the words can be changed. The original words of the American national anthem, "The Star-Spangled Banner" were a hymn "To Anacreon in Heaven". Here is a version of the original:
So while you might claim that, for example, the Brandenburg Concertos of J. S. Bach are "about" the relationship between the individual and society in the 18th century, it is mostly speculation. And even music with words, like his cantatas, was often taken and used to set entirely different words. Music originally written for use in a Lutheran church, was re-used to set the Catholic liturgy.
And you can be sure that just about any catchy classical piece will sooner or later end up in a commercial for an airline--or Gatorade!