Freedom of speech means that if we both share a public space, then we have the right to express opinions without fear of punishment, attack, or penalty.
Interestingly like most freedoms, this freedom is normally protected by rules. without these protective rules the freedom collapses into abuse.
We can display information on something we own eg a Tshirt, but not on a wall - which we don't own.
Most shared space has rules so as not to make it too unequal. For example in my country you can speak your piece in the street, but you may not amplify your voice with a loudhailer or megaphone, if anyone objects.
(I once phoned police and complained about a Christian ranter using a loudhailer and they were on it instantly and thanked me saying they coudn't act until I complained.)
But this is PUBLIC space where neither side has ownership.
Club space is a bit different and like membership itself, is subject to the rules or decisions of the owne, or managing committee. (This is like forums.)
Spam in my Inbox is invading my PRIVATE space. Public free speech does not apply.I have the right to decide who can speak to me in my home and my inbox is like an online "front room."
(In both cases certain authorities, emergency services, police and other government agents, can enter and speak against my will.
In our Inboxes must negotiate what we permit each other individually. What one person permits eg swearing, slang, *****y gossip, porn pics, sexist jokes, another does not.
In the EU I believe it is now law that sales emails should only send to opted in addressees, and even so contain an Unsubscribe link. Trouble is spammers easily host their email outside the EU.
A forum is controlled, owned space, even if "open to the public." They are by their nature authoritarian. The owner may PERMIT a lot of freedom but by the nature of the software we are dependent on the owner/ mods to allow us our freedoms. They are like pubs and restaurants, open to the public but under private rule.
We state in our rules that sales messages such as mass spam are not accepted, so spam is against the forum rules.