It's interesting how we celebrate that capitalism instills competition that leads to global improvement for everyone, yet we like to hand-pick the segments of capitalism where we want competition and the segments we don't want competition. An NDA is one case of this, as are non-compete agreements, and many behaviors within cartels, say when Apple et al conspired to not hire each others labor.
Usually, this hand-picking is performed by those succeeding the most in the given system because they have resources and leverage to dictate such terms and force them on others, yet another anticompetitive behavior. The fact is that most people just celebrate capitalism when it benefits them and reject it when it doesn't.
Personally, I think any such agreements should be illegal. If we had more labor unions where the labor force organized and created their own anticompetitive behaviors to counter balance the leverage of large capital holders, then I'd be far more sympathetic. Such is not the case and the labor force is on a near Darwinian level of competitiveness so I have no sympathy for any sort of anticompetitive behaviors from businesses.
To be clear, I understand how this perspective blows up many business models, but it has also blown up the livelihoods of many of us in the labor force on this push to commoditize labor for the goodness of whatever. I say, why don't we commoditize these business secrets for the same unknown goodness? Why is it we keep picking and choosing who gets breaks on competition and who doesn't. Let the markets decide.