Four pages for something so simple...
First, this is not a public forum, it's a private forum. The forum owners can proscribe whatever behaviors they choose, except where, as Jafo mentioned, this forum may be required for customers to exercise their rights.
The above aside, there are 2 competing factors.
One is that we are responsible for our behavior. Many talk about 'freedom' but they leave out the other half -- responsibility. Together, it's 'with responsibility comes freedom' -- if we behave responsibly (including following any rules the forum owners have), we then have freedom to post as we wish.
The other competing factor is how we react to things. Dad used to say 'the less you expect of others the happier you'll be'. Dad was a wise man. If we expect others to behave in certain ways (such as to not troll) then we're setting ourselves up to be unhappy.
Were dad around for internet trolls he'd not give them a first thought, let alone a second thought. Not merely 'sticks and stones...' but even that would be giving trolls more thought than they merit.
Were I to give thought to a troll it would be to tell them 'an insult from an idiot is a compliment, so thank you!'. But I'd only do that because I enjoy giving idiots the opposite of what they want. I'm not as wise as dad was
Being human, we have the ability to keep these 2 competing ideas (holding people responsible for their actions, and not expecting others to behave in certain ways) in mind and resolve them.
So, this whole thing is really pretty simple.