It is more about freedom of speech than privacy. Whose privacy are we talking about?: That of a confirmed terrorist who has already killed tens of innocent people. Enough “probable cause” there. Also, there is a compelling interest in tracking down his connections to save future lives. Apple is comparing an iOS specially made for Syed Rizwan Farook to some sort of biological weapon which, once made, may leak to threaten the whole world or at least will remain indelibly in the coders’ memory to pose a permanent threat to the world’ iOS users. However, given the Apple coders have capabilities to do so at any time, the increase in risk does not seem that great.
What is more important is whether Apple can be forced to code for anybody just as Alibaba can be forced to yell “Open Sesame”. Asking Apple to write a single-device iOS is different from asking a safe company to make a new key for an old long forgotten safe. Coding is not a physical act but an intellectual act. It is like painting, writing, sculpting, orating, etc.
Right not to be compelled to speak is not absolute. American courts routinely lock up people for refusing to testify in court, most famously, Judith Miller. The public interest in pursuing truth in a publicly sworn forum overrides the witness’ right against compulsive speech. However, coding is creative activity, more involved than simply giving information. If Picasso cannot be forced to paint for Franco or a republican, Apple cannot be forced to code for DOJ.
No matter how overriding the public interest is, coding or invention cannot be compelled. Coders have absolute ethical rights to refuse to write the ethical equivalents of Volkswagen emission manipulation software. DOJ can ask but cannot compel Apple to write the software. Apple’s refusal is an ethical stance that should be respected.
The coin side of calling this ethical is that Apple should be also respected if it decides to cooperate. Probably, Apple know this by now. My guess is that Apple will probably give in.