A non-disclosure agreement would, in my mind, violate the inalienable rights protected by the Constitution. Freedom of expression is protected by the 1st Amendment, and is considered an inalienable right.
On the other hand, if you sign a non-disclosure agreement, and fail to adhere to that agreement, then you may suffer consequences to your reputation. Social pressures can be enough to keep you in compliance with the NDA.
For every individual bound by an NDA, they must weigh the costs and benefits of adherence. For the women who are willing to violate the NDA in order to testify against Trump, they stand to gain enormous benefits in so doing. For the lowly employee who is a party to an NDA, he will suffer a blow to his reputation should he violate the NDA.
So the question is not whether one can or cannot blow off an NDA. The question is whether or not one is willing to suffer the consequences or enjoy the benefits of violating and NDA. It all depends on the context.
To put it differently, manufacturers who pollute the environment consider the cost of compliance and enforcement as a cost of doing business. To many manufacturers, the well-being of the community is a secondary concern (just think "DuPont").
Whether one chooses to honor a contract has more to do with the political and social power of that person than probably, any other factor. So sure, a woman who has suffered abuse from Trump can become an instant celebrity. A few talk show appearances and a book deal will more than compensate for the potential damage of violating an NDA, and in that case, these women "can get out" of an NDA.