Those of us living in the United States are protected by the wonderful First Amendment, which provides us with freedom of speech. Businesses like Facebook can still block you if they want (thanks to their First Amendment rights), but you’re free to publicly say most anything you want (yes, including yelling “fire” in a crowded theater).
That said, just because we’re legally protected doesn’t mean it’s always wise to just spout opinions without defense. In Think Again, author Adam Grant puts it like this:
When we find out we might be wrong, a standard defense is “I’m entitled to my opinion.” I’d like to modify that: yes, we’re entitled to hold opinions inside our own heads. If we choose to express them out loud, though, I think it’s our responsibility to ground them in logic and facts, share our reasoning with others, and change our minds when better evidence emerges.
I agree with Adam that you are 100% entitled to your opinion. When that opinion goes against logic and facts, and you continue to hold your position, it tends to look pretty bad. I find that the smartest people tend to change their minds and are generally happy to do so. If you have something that you feel strongly about, do some digging to see if the facts and logic support it, and then decide on your next steps.