There are no 1st Amendment rights in a forum like this.
Now, and it's because I follow the Civil Rights Lawyer, there are some exceptions.
The 1st Amendment protects you from government taking away your right to free speech.
Now, where it could involve a forum like this, there have been cases where someone will go on a governmental Facebook page and write something negative about that governmental agency. For example, if you were to go on Portland Police's FB page and say that they were wrong for shooting someone, and PPB deletes your post, that violates your 1st Amend Right.
But no, you do not have 1st Amend Rights in this forum.
Just like Jimmy Kimmel doesn't have 1st Amend Rights against ABC, his employer. He might have a case against the FCC and the Trump Admin but that is beyond my 1st Amend knowledge.