The legal standing and precedent is established based upon the expectation of privacy in the first place. When you enter a public forum or social network or web page for that matter, there is no expectation of privacy. Any information about your activities wanted by any government agency SHOULD be obtained with a warrant, alas, in today's day and age, it happens more without one than with. You'd be surprised what you'd learn if you did just a little research into the subject.
Recent laws are being stretched to make it easier and easier to perform surveillance on your activities, illegal or otherwise. Warrantless location requests to mobile carriers are at an all time high. Data gathering has been a quiet back door industry for years here and little of the populous are paying attention. The federal government and with the support of local law enforcement are pushing through laws requiring ISP's, mobile carriers, search engines, etc., to save your online activity for a period of 7 YEARS! Now what would they need that for? Anyways... That's for another rant, lol.
But there are ways to combat it if you really want to go through the efforts of being paranoid...
Encryption is the key, and judges give little sway to law enforcement that wishes to break into something that's encrypted WITHOUT displaying or substantiating a SUSPICION of illegal activity, not just hunches! If encrypted, there is no way for them to see by just browsing what's on the surface and available for all and or anybody to see. Same with cell phones, lock them, period! Yeah, a pain, but necessary. Pretty Good Privacy works...
Simple is, simple does... Recent Supreme Court ruling in Cali (I think) it was stated quite clearly that your RIGHTS are not a given and that you must CLAIM/ASSERT them if you want them, period! No simple disclaimer does that. I laugh every time I see one of those posts (OP) and so does 'they' who are watching!
Lolz

Regards!