You have absolutely no idea what you're talking about. By your logic, I could hire someone to put an ad on television for me and I'd have no recourse if they instead make an ad for a competitor or make an ad that's just one long "FUUUUUUUUUUUCK".
All freedoms have limits, none are absolute. Freedom of speech, for example, does not include:
- The right for you to place others in immediate danger as a result of your speech (e.g. the "yelling Fire in a crowded theatre" example)
- The right for you to damage others' reputations through telling of falsehoods (libel and slander)
- The right for private property owners to give you a platform -- I can kick you out of my building for your racist speech, but I can't kick you off the sidewalk
And those are just a few examples. The fact that you have freedom of speech means that you have the free choice to enter into an NDA or not. You cannot be coerced (this would invalidate the contract) to do so, and NDAs have to be limited in scope (you can't talk about this thing, specifically) and duration (I can't prevent you from talking about it forever).
Your ideas of both constitutional and contract law are incredibly naive.