The US Supreme Court is going to be discussing the legal doctrine of first sale today, in a case that has something to do with school textbooks but will ultimately have further repercussions. Your right to first sale means that you are allowed to sell on books and DVDs that you bought. However publishers are attempting to license, rather than sell, such materials, and these end user license agreements seek to prevent such selling on.
I find it hard to agree with either side in the debate. On the one hand, if you want to sell on a book that you bought in a book shop, this should not be answered with violence. On the other hand, if you write a book and want to sell it on the condition that the buyer does not then sell it on to someone else, this should not be answered with violence. What if you attempt to make this agreement and the buyer then breaks it? Refuse to deal with that buyer again and tell all your friends. Not practical? Consider alternative business models. The state should neither uphold nor prohibit specific business models, and I suspect it should not be involved in contract enforcement either.
For a publisher there are plenty of non-violent solutions, such as encryption, digital rights management, watermarking, subscription services or being so awesome that everyone wants to throw money at you.