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If someone re-mixed music I made, sold it, and tried to restrict further re-use of that derivative work, I'd be furious!
I would then call my lawyer, and invoke the justice system to bring them in line, and probably re-allocate their filthy lucre to X or some other software project.
I wouldn't have a problem with selling it, that's a right granted by the license I chose. It's the re-use that's also granted to 3rd parties.
Same with software I'm involved with. See the recent BusyBox case(s).
Ideas are licensed.
Copyleft only works because of how (arguably over-)strong copyright became after 1976.
Similar ideas apply to patents, but the patent system is borked atm.