It depends upon the association you have signed into, for a detailed breakdown on the legalities pertaining to Associations read this.
On an open site, one has to back up their comments and be able to take criticism as much they give it.
If comments are based upon fact they should be corroborated in the text to provide a clear picture of exactly what happened or what is being written about. Perhaps it would make it a more fair comment is to do exactly that.
Freedom of speach is and should be allowed if the domain within which to present your rhetoric is open.
The lines drawn are usually based on refraining from bad lanquage, certain images etc.
Other than that I would prefer comments to be about decking the timber or composite type and not that of someone that has disagreed with you.