"Authoritarian country" is too prone to no-true-scottsmanship. So I'll just say that it's fairly common in the U.K., and definitely not unheard of in the U.S. E

"Authoritarian country" is too prone to no-true-scottsmanship. So I'll just say that it's fairly common in the U.K., and definitely not unheard of in the U.S. Even if someone legally should not be arrested, people are people, and the police will often detain someone just to be on the safe side, when responding to a complaint. Putting something on Facebook opens you up to complaints from a potentially wide audience of lurkers who may not understand the context of a post, or worse, might be angry with you and looking for petty revenge. So, people do get arrested for Facebook posts in practice, regardless of whether it is legal to post the content.