The “
first sale doctrine” in the United States allows lawful owners of copyright protected books and CDs to transfer (by sale or gift) without permission or any further payment of royalty.
Now, this is not a new doctrine – this has been recognized by the Supreme Court since 1908 (and is codified in the Copyright Act of 1976 as well).
So anyone publishing in the US is aware of the rules – and thus implicitly consents to them. This is part of the compromise made in receiving an exclusive copyright franchise. It is hardly unethical to exercise it – all parties involved were aware of the rules.
If you feel that buying used goods was unethical, then you would also be compelled to believe that libraries (public libraries, school libraries, church libraries, university libraries) are unethical as well (in US law, this is the
fair use doctrine, and is stronger than the first sale doctrine). Indeed, you might even argue that teaching is unethical as well, since teachers often present material gathered from other sources and present it to students.
But all civilized societies, and all religions, and all schools have recognized the value of both libraries and teaching. This seems to be a universal value. This strongly suggests that there is nothing inherently immoral about either the first sale or fair use doctrines, and therefore we should obey the law of the land.