It is right that all social media users are aware that law enforcement agents might be able to access internet material that they believe to be private. This is particularly the case in regions such as Saudi Arabia where groups such as women and homosexuals are at risk of severe punishment for activities that many people would not classify as a crime.
Social media in the Middle East is a very dangerous thing. Users of these sites should know that the government can view and use anything that they post as evidence against them. This may cause users to post a lot less, but then they at least know the risks of posting possible incriminating things online.
There are disclaimers used for all different aspects of Internet usage. I don't see why this should be any different. Many people using the Internet are not informed of who sees what. They just take the Internet very casually and think everything is safe. Although, would they actually read the disclaimer?
It is completely unnecessary for social media sites to provide a disclaimer that states the Saudi Arabian government may view user posts to prove illegal activities. Users of social media should assume that anyone can view their posts and should post accordingly. If they post information about illegal activities they must assume that they expose themselves to risk of disclosure to governments or others that may prosecute them