Part of me wants to say that in a truly just society, civil disobedience would be unnecessary and leave it at that, but that approach seems a bit simplistic.
The question I would add to Joel's is this: Are rights and duties necessarily exclusive?
In the case of some other rights, I would say no. For instance, I believe that voting is both a right and a duty for any citizen who cares about the state of their country. On the other hand, there are rights for which this is not true -- I certainly would not say that we have a duty to bear arms, or to remain silent while being arrested.
In short, my response to Joel is that, in a just society -- or even a society that strives to be just -- citizens have both the right and the responsibility to civilly disobey if the society ever leans towards injustice.