To many librarians, a boycott may seem counter-intuitive as it will in practice prevent patrons from accessing some Macmillan books from the library. We do not take this decision lightly, and we agree that librarians should support access. Unfortunately, the choice not to boycott also impedes patron access. If we simply capitulate, we effectively communicate to other publishers that embargoes are acceptable.
Source: Editorial: Why We Choose to Boycott Macmillan E-books