That's a matter of opinion. I believe in the moral rights of the creator to control (to some extent) and profit from their work, but not at the expense of the public's interest-- copyright law exists and establishes the existence of "intellectual property", as an artificial monopoly, not as an extension of human rights but to promote the public's interest in the creation of artistic and literary works.
I can't advocate forcing publishers to spend money on keeping a product in print that they don't wish to keep in print-- for financial or moral reasons-- and when it comes down to it, I can't really advocate forcing them to keep a digital product available through an online retailer if they no longer wish to be associated with it.
But... I do think their decision to stop selling a product, whether or financial or moral reasons, should absolutely terminate their artificial legal right to prevent others from doing so-- since the moral purpose of copyright, after all, is to encourage the public availability of cultural works.