Your 'freedom of speech' applies only in a public place. Even then, spreading rumours about someone to harm their reputation is illegal. It's called slander and libel.
But this isn't a public place. It's private. You requested to be here. And being in a private place, you really have no rights. Particle, and those he assigns the power to, is free to do whatever he wants with your posts. By posting here, those posts become his property.