They don't. They have some rights, not all. https://constitution.findlaw.com/amendment1/free-speech-rights-of-prisoners.html https://constitution.findlaw.com/

They don't. They have some rights, not all. https://constitution.findlaw.com/amendment1/free-speech-rights-of-prisoners.html https://constitution.findlaw.com/amendment1/free-speech-righ... "A prison inmate retains only those First Amendment rights that are not inconsistent with his status as a prisoner or with the legitimate penological objectives of the corrections system." i.e. if restricting freedom of speech is consistent with that, they would be restricted. Not all forms of speech restriction are consistent with that (and if the state tried to restrict those, the courts would probably overturn it), but to say they have the same free-speech rights is objectively false. In this case, it would seem that the legitimate objectives of the correction system would fit with restricting his speech (as the OP states, it probably be better if he didn't do that).