Acts in public are not protected. This, however is:
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
Posting on a publicly accesible website is the legal equivalent of standing on the street corner having a conversation. A police officer doesn't need to search anything because it's out in the open.
A conversation is ephemeral unless someone specifically goes out of their way to record it. That is not true by default for just about anything involving a computer and we all know it. Where's the line between obtuse and lying?
"The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.