Because, it seems, the right of privacy (I would assume the shopping mall asserted that as owners they had the right to determine what was allowable on their premises and no one else) is held as the preemninent of the Bill of Rights. A first, among lesser, equals, so to speak.
Free speech (which would mean, you can say it, but no one is compelled to listen to it)? Only in your home, because you have ultimate rights there.
Freedom of religion? Only in your home, for reasons mentioned above.
Right to bear arms? Only in your house (but some are hoping to change that).
Right to assemlby? Not necessarily in your home, because it might offend your neighbors (reference house church groups which are specifically banned in some locales).
Right to privacy? Not if your thoughts (assuming they do not advocate that which is unconstitutional/treasonous) are politically incorrect.
One can argue anything. But until one tries to parse the competing considerations, constitutional, public policy, and plain old common sense, in a thorough anjd even handed way, one isn't contributing much of anything.