That's exactly the problem and why anyone providing this kind of facility has to moderate and remove such content promptly.

That's the point.
The content would be taken down.
And that's what happened.

The question is whether the site should be shut down if this happened and the content was then removed?

Should the police have the right to seize every single server that is mirrors the offending bulletin board?

It is important to be clear about how Indymedia differs from other news organisations. Indymedia provides a platform for people to speak freely at the same time as guarding their anonymity. It does this on principle, and its systems are configured to promote this by not recording IP addresses. See http://www.indymedia.org.uk/en/static/security.html and http://www.indymedia.org.uk/en/static/privacy.html

The question is whether _this_ freedom should exist and be defended and if so, what limits should be set on that freedom.

I think the freedom is worth defending. Certainly if you live under a repressive government, this capability may be essential to protect people who want to report on that repression. Whether the UK is or is not repressive is disputed, but if this freedom is defended, it makes it harder for it to become repressive. For this reason, Indymedia should be free to provide the service that they offer without unreasonable interference - they should also have a duty to behave responsibly.

The downside of this open publishing approach is that the platform might be abused by some in ways that threaten the rights and freedoms of others (as in this case). There is a need to moderate and remove abusive content. Indymedia acted promptly to remove the offending post.

If Indymedia should be free to operate as they do (no-one has brought legal proceedings against their right to work in this way), and they behave responsibly in terms of moderating abuses (which they have), then they should be allowed to do so without interference.

I have no sympathy for SHAC, but I am glad that some people give up their time, energy, money and equipment to enable our right to free, anonymous 'speech'. I think these volunteers deserve similar protections against interference as do commercial journalists and publishers.

They did act responsibly. They removed the offending post as soon as they became aware of it and BEFORE they were contacted by the police.

The police did not get a warrant.