In reply to elsewhere:
I agree it is a practical issue when the law is unclear and forum owners legal responsibilities are unclear in this respect. In the absence of clear guidance threats of legal action against forum owners can flourish and be successful in having posts removed even if those posts might be factually true or at least not untrue which is a way of suppressing freedom of speech.
Not having clear legal guidance in how a publisher is legally different from a platform is I think not helpful to forum owners or in the public interest.
I imagine there are individuals and organisations that champion freedom of speech would be supportive of a suitable test case.
In the absence of clarity it is prudent for forum owners to be suitably insured and/or put the forum in a limited company so liability is limited.