Please don't get mad at me, OP. But every point you have made about "just" and "unjust" opinions are, in the end, just your own opinion. Unless it is involving something that can be proven or disproven with hard facts, no opinion is really right or wrong. An opinion that may seem "unjust" to you may be perfectly "just" to someone else..

This discussion, in my OPINION, is best described as an endlessly long snake that will forever devour itself.

The word 'instead' doesn't matter. If he doesn't like the content of the song, then he doesn't like the content of the song. Somebody not liking the subject that a song is about is not "unjust".

An innocent person being imprisoned is unjust. Somebody not liking a song that you like is not unjust.