Copyleft is a movement which differentiates itself from open sourcing and copyrighting. While the open source idea is to allow free access (”free” as in “freedom”, not as in “free beer”), the danger lies in someone improving it and then copyrighting it. On the other hand, copylefting a product means that it comes with a condition that no improvement of it shall ever be copyrighted, but will always be available free to engage with.
The debate on the legality of downloading music is a point of intervention for those who seek a world freed from the capitalisation of human history. The legality claims that downloading is a criminal activity. The assumption here is that the material (concept, idea, the artistic product) is a result of individual talent. However, this line fail to notice the role of tradition in individual talent. To be precise, what is yours is yours but also not yours, as you call into service the results of centuries of human effort that went to it.
Copyrighting invests all rights in the creator or the marketor, or whoever possess the right. Thus it cordons of the rest of the humanity from appropriating it. Copyrighting, and stringent actions on its violation, can ensure that no penny of the royalty is lost, and the artist is compensated for the eerie hours, the delirious afternoons, the sleepless nights. But downloading can help too, if it is done with a political conscience. It can pressurize the corporate giants to bring down their pricing. It helps the art to reach beyond those who can afford. And it ineviatble makes the artist more popular. And, ultimately, it makes illegal downloading a thing of the past.