The first amendment means that the government(s) cannot prosecute you for what you say. But there are exceptions:

- You can be prosecuted for the effects of speech, e.g. inciting people to riot/commit crimes;

- Threats of violence are not protected;

- Misleading claims in advertisements are not protected;

You can still be sued in civil courts for libel/slander, or the effects of your speech.

And people have the right to shun you if they don't like what you say.

It does not mean that a publisher is obligated to publish your speech. A newspaper does not have to publish your letter, a blog can delete your comments, and Facebook or Twitter can delete your posts or even suspend your account.