Putting aside the legal aspects and ramifications of illegally downloading music
The notion of "intellectual property" is fraught with difficulty, and my first reaction to this kind of argument is to question whether there is any such thing. Indeed, there are intelligent and thoughtful people who do precisely that. See, for example, this post by Richard Stallman.
But one does not have to go that far to think, as many more people do, that copyright (and especially patent) law has gotten completely out of hand. Most people seem to think that copyrights and patents exist to protect the rights of the creator of the work in question. This is questionable. One might hold instead that they exist to further society's interest in encouraging creativity and innovation, and that the laws governing so-called "intellectual property" ought to based upon an understanding that this is, indeed, the sole legitimate purpose of such laws.
So, if we value the creation and production of music and wish to encourage it, we would do well to think about what a sustainable and rational "business model" for musicians, composers, and the like might be, one that is compatible with the rights of the rest of us and that will, indeed, further the goals that matter to us. It seems clear that the model that was in place fifteen years ago is no longer workable, and many musicians have already shifted direction dramatically. For example, bands used to tour to promote records: Tickets were the loss-leader that drove record sales, which was where the money was. Now, bands release records to promote their tours: Tickets are more expensive, and that is where money is made. That, indeed, is the model that was in place seventy years ago or so, and it is the way the great majority of musicians make their money. (Composers and the like are a different matter. But I'll leave their plight to others to speculate about.)
It's worth appreciating, too, that the large record companies are really no friends to musicians, but on the contrary have been exceptionally exploitative of musicians, and they have sought to control music in ways that, so far as I can tell, serve no-one's interest at all.
Well, I'm not sure I've addressed the moral question, but I guess that's because I don't think there is a moral question here, unless you think there is some kind of "natural" right to intellectual property. And that's precisely what I don't think. I think property, in general, but especially intellectual property, is really a political and legal notion, rather than a moral one.