You can indeed legally sell your old CDs in whatever venue you choose.

Ownership of the copyright — the rights in the contents of the CDs — and ownership of a physical CD are two distinctly different things. For example, when you purchase a Michael Jackson CD, you own the physical CD, but you don't own any of the rights in Michael's music other than the right to listen to your CD.

The copyright holder is entitled to receive payment for his/her music, but only one time per physical CD that was produced under a license granting the producer the right to distribute the content of that CD in exchange for money. Once that CD is purchased, that royalty is paid and the physical object belongs to the new owner, to do with as s/he pleases.

iTunes (and other digital) content doesn't come in a pre-packaged physical device. To sell (or even give) that content, you necessarily must make a copy of it, whether that copy is onto a CD, onto a flashdrive, onto an emailed file, onto whatever. The minute you make that copy for distribution (not sale; distribution. Money is not a factor here) without license from the copyright holder, you are creating an illegal copy of the file, and that act of copying infringes the copyright in the music.

Reselling a physical, licensed CD that you purchased doesn't involve copying the files contained on that CD. That's the difference.

THIS POST CONTAINS GENERAL INFORMATION AND IS INTENDED FOR ENTERTAINMENT PURPOSES ONLY. IT DOES NOT CONSTITUTE LEGAL ADVICE, NOR DOES IT CREATE ANY ATTORNEY-CLIENT RELATIONSHIP. FOR LEGAL ADVICE ON YOUR PARTICULAR MATTER, CONSULT YOUR ATTORNEY.