Legal rights are conferred by law, and would not exist if not for law. The right to run for President is a legal right, because the office of the President would not have existed if not for the U.S. Constitution.
Natural rights, on the other hand, exist regardless of law. Nobody is supposed to rape you, not only because the law says so, but also because you have a right to decide who you have sex with. If the law does not prosecute rapists, the law is wrong, and you still have the right.
The U.S. Constitution is remarkable not only because it created (legal) rights that didn't exist before, but also because it finally recognized so many (natural) rights that used to be blatantly ignored by despots.
Of course, whether "freedom of information" is a natural right or a legal right is a contentious matter. Most likely, it has components of both.
Government is a set of people, and rights arise from consensus and practice among those people. When the Founders spoke about "rights" they were referring to those recognized by British consensus and practice.
This is unfortunately common, so that most freedoms cannot actually be realized without the help of law and the judicious use of institutional force, far beyond what I or almost any citizen can personally wield. And it is not even vaguely exceptional that the source of the problem is coming from non-governmental entities.
Law is much more than "a set of people."
I think it's fairly clear that the Constitution is also intended to restrain non-Governmental entities from violating personal rights. Otherwise, the 13th Amendment would only make Government slavery unconstitutional while reserving it to the states or the people, which would be nonsensical and useless.
The rights of plantation slaves have surely existed all along, but they didn't make any difference until a lot of blood was spilled to change things.
That's question-begging a bit. If I hire you for my radio show and you say something stupid on the air, am I not allowed to fire you, lest that be a violation of your personal right to free speech? If I refuse to sell you a gun, am I denying you your right to bear arms?
Otherwise, the 13th Amendment would only make Government slavery unconstitutional while reserving it to the states or the people, which would be nonsensical and useless.
That seems to argue against point. If the whole Constitution was meant to restrict non-governmental actors, then they wouldn't have limited it just to slavery.
Also, the Fourteenth Amendment generally applies the restrictions on the Federal government to State governments. I'm unaware of any restrictions it places on non-goverments.
http://en.wikipedia.org/wiki/Pruneyard_Shopping_Center_v._Ro...
America, in spite of its contradictions, was to a significant extent based on the idea of "inalienable rights", and is why it was so successful. The verbiage in The Bill of Rights was intended to recognize, not confer rights, and it was intended to restrain government from violating them.