The issue with Sonny Landham isn't freedom of speech, but freedom of association
Freedom of speech does not mean that others must provide a platform for your speech; the same applies to all other freedoms. You have the right to life, liberty and property, but that does not mean others must guarantee your life and liberty, or provide you with property. Having the rights simply means that you and your defenders can legitimately go after those who violate your rights. But others do not violate your rights just because they won't let you join their group, won't let you borrow a printing device, or even not participate in protecting you and/or your home. It comes down to a private group's members' right to freedom of association, which is an extension of the rights to liberty and property. They have every right to refuse to permit someone's association, depending on enforceable agreements like contracts or by-laws. Likewise, members who think the group is wrong can themselves leave and form their own.