The First Amendment of the Constitution of the United States reads:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.Note that this does not say "people are not permitted to laugh at your free speech and to call you an idiot." You have the right to speak your opinion. You do not have the right to expect people will agree with you. They may call your beliefs into question: they may even call your sanity, your morals and your parentage into question. You can respond in kind, or you can choose to ignore their responses. But you cannot expect the government which protects your freedom of speech to impinge on theirs.
Freedom of speech involves accepting responsibility for the consequences of that speech. If you use your freedom of speech to make libelous claims about your competitors, the First Amendment does not stop the aggrieved from suing you for damages. If you hold unpopular opinions, you may not be jailed for speaking your mind. But you may lose your job or your standing in the community: you may lose the respect of your friends and colleagues. And the First Amendment will do nothing to protect you.
(There are certainly other laws which might do so: if you are fired for exposing your company's illegal perfidy, you may be protected under various "whistleblower" laws, for example. But if you posted a long rant about how your boss has his head so far up his ass that he parts his hair every time he breaks wind, don't expect a lot of sympathy from a judge or jury when you sue to regain your position. And while you may have a case if you're fired because of your religion, that case will be considerably weakened if your religion involves a belief that you have to preach to your students in a public school).
Mel Gibson did not go to jail when he declared that "The Jews are responsible for all the wars in the world." But many people regarded his statement as offensive and stupid, and it certainly didn't do good things for his career. Tim Hardaway was not charged with a crime when he said in an interview "You know, I hate gay people, so I let it be known." But he was widely criticized and mocked for his ignorance. (Perhaps the best response came from George Takei).
Words have power, to heal and to harm. While the Miranda warning only applies to arrests in criminal cases, it contains one phrase which is worth remembering: "anything you say may be used against you." Don't speak unless you are ready to accept the consequences of your speech, and don't assume that today's stupidity won't come back to haunt you tomorrow.