There is often confusion about what the First Amendment to the U.S. Constitution actually protects.
Among other protections, it prohibits the government from making laws that infringe on freedom of speech or freedom of the press. The government can’t tell you what to say or not say, nor can it tell a newspaper what to publish.
However, this does not apply to a private company or group, nor to an online forum or a reader comments section. It only applies if the government is doing the prohibiting.