I'm a web admin, so perhaps this might be of use. The rule of thumb is that matters of opinion can be protected as free speech, whereas practical information on making explosives, 3D printing weapons, how to groom children for pedophilia, release of personal information on members, etc is not protected because it threatens the rights and safety of others.
However, not ALL opinions may be protected, especially on a private website (i.e. privately owned). This board, like many, is subject to rules not unlike those encountered on entering a private residence. IOW, you are expected to obey house rules, follow a certain etiquette, or you will be asked to leave. Personal attacks, even though they may be opinions, may not be allowed. And, as in a private home or a club, there may be other rules, such as requiring some support for statements presented as resting on fact.
One common misunderstanding is when a member cries foul because they think their message board is a public platform, like a soapbox in a public park or square. B-but,
FREE SPEECH! Then it has to be explained: You are on a private website. You are essentially a guest in someone's home. You can't walk on our carpets in your muddy boots, you are not completely free here.
Point being, if you value intelligent discourse more than the cacophony of the ranters in the park, then there have to be restrictions on your speech. Otherwise everything is dominated by the loud and stupid. C'est la vie.