Copyleft and copyright are not at odds. To promote copyleft, you exercise copyright. Furthermore, copyright is key to ensuring attribution, and attribution is

Copyleft and copyright are not at odds. To promote copyleft, you exercise copyright. Furthermore, copyright is key to ensuring attribution, and attribution is an important enabler and motivator of creativity (copyleft does not at all imply non-attribution, in fact copyleft licenses may require it).