One last perspective on annotation from a technology point of view. One of the themes of this essay is follow the effects, not the technology. In this case, the effect of annotation technology is identical to what could happen if someone hacked into a web server, and installed software onto it that would cause it to provide annotation services to people who used it from that point on. That would literally change the contents of the server.
For people using the annotation programs, the effects are identical to the server serving out changed content. Yet nearly nobody would claim that this is legal or ethical. But this is really a contradiction; two things with exactly the same effect, yet one is ethical and one is not?
So, follow the effects. If it looks exactly like the content on the server is being modified, then treat it that way. If it looks like the server is being hacked to provide this service, then treat it that way. Otherwise, we open a loophole that will allow people to "hack" servers without hacking them, by riding the line between what even current law recognizes as illegal access and "allowed" annotation. For example, suppose I own a computer that a certain website uses as its connection to the Internet, so all packets that computer sends must go through my machine. Suppose I configure this machine to dynamically add a nasty picture to that machine's home page every time someone accesses it from the Internet. This looks exactly like somebody hacked the machine to include that nasty picture, yet it's all done by hardware I legally own, and if we're to allow arbitrary additions to the chain of responsibility, you are left with no real way to call the action unethical communication behavior. Yet we would certainly all feel this is highly unethical.
It is a testament to the consistency of the model we have built so far that three different ways of looking at the issue (as censorship, as insertion onto the chain of responsibility, and from the perspective of effects) all have the same result: Annotation should not be allowed.