If you think he did something illegal, report him to the police or sue him. If not, then this is freedom of speech.
…and? People also have freedom of association, and people can choose not to associate with an organization that employs someone with morally awful beliefs - especially when they make those beliefs very public.
Apparently, Stallman is a net positive for them, so they keep him.
Doesn’t mean that they in any way endorse pedophilia.
And the freedom of association also doesn’t mean that a bunch of enraged people online have the freedom to decide whom they associate with.
And apparently, in the USA there is a whole party devoted to child marriage and other ways to have sex with minors. That might be the better point to start, because they actually have a say regarding laws on that matter.
