The option of making downloading illegal is a central issue. However, whether or not there is illegal downloading, that will never prevent copies of musical works from being made, in particular using all the CDs that are bought. Music copying is a recurring phenomenon.
However, if buying music on line was the only option in the world, part of the problem would already be solved, but that would not prevent copies from eventually being made. So compensation must be paid for those copies because they have value.