If an author declines authorship, may her co-authors publish without her? This question was raised in discussion of answers on Is it better to submit a paper to an important journal without the supervisor name or to a less important journal with the supervisor name?  There seemed to be a significant difference of opinion, so I'm asking it here as its own question.  I'll phrase it as a hypothetical.

Suppose that researchers X, Y and Z have collaborated on a project.  Each has made major contributions which were essential to its success, and would ordinarily be entitled to co-authorship on the resulting paper.  However, X decides, for some reason, that she does not wish her name to appear on the paper, but she is willing for Y and Z to publish it under their names alone.  

May Y and Z ethically do so?  

Of course it seems clear that X must consent to have a paper published with her name on it, and she has the right to withhold that consent.  It's less clear whether Y and Z may publish anyway, effectively claiming credit for X's work, even though she consents to them doing so.  It could be argued in this case that Y and Z may not publish the paper at all.

Another possible concern is that, if X has the right to decline credit for her work, she could be pressured or coerced or bribed into doing so, effectively reducing her to a ghost writer.
It seems to me that if authors B and C write in the acknowledgment section that the contribution of person A was sufficiently important that they think A should be listed as an author but that A declined and especially if authors B and C provide a description of the reasons leading to A's refusal which is satisfying to A, in other words if B and C report accurately what has been happening, then no one is behaving unethically.

For a real life example, one can look at the acknowledgment section of S.Bloch and K.Kato's work on p-adic étale cohomology, the third author being in that case O.Gabber and the reason invoked (if I recall correctly) being that Gabber did not think the work was ready for publication (I'm unable to track the precise reference at the moment, it is not Bloch and Kato's article at the IHES in 1986).

UPDATE: Because I haven't been able to track the reference of Bloch-Kato, let me point out Beilinson-Bernstein-Deligne which starts with


  Il avait d'abord été prévu que O.Gabber soit coauteur du présent article. Il a préféré s'en abstenir, pour ne pas être coresponsable des erreurs ou imprécisions qui s'y trouvent. Il n'en est pas moins responsable de bien des idées que nous exploitons et le lecteur lui est redevable de nombreuses critiques qui, nous l'espérons, ont permis d'améliorer le manuscrit.


which roughly translates as 


  It was first planned that O.Gabber would be coauthor of the present article. He chose to abstain, so as not to share the responsibility of the mistakes or imprecisions to be found in it. He is nonetheless responsible of many an idea we exploit here and the reader owes him numerous criticisms which, we hope, allowed for improvements of the manuscript.