The idea that ideas have no value is prima facie ridiculous. The reason we aren't just a slightly odd species of chimpanzees is that we developed the ability to produce ideas. Ideas are the only thing of fundamental value to us as an intelligent species.

The statement that ideas don't matter, only execution matters, can only apply among sets of trivial ideas that don't change the landscape. Yes, if you want to make Facebook for Farmers, that's an idea that is completely interchangeable with hundreds of other equally trivial ideas, and it doesn't matter which one you choose so much as how well you execute on it. But if you have a genuinely significant idea, something that can fundamentally alter the landscape or advance humanity, then execution is secondary, and, in fact, lots of different people or organizations could implement it. That isn't to say that you can't screw up the execution and fail thereby, but the limiting factor to success is different for trivial ideas vs significant ideas: there are thousands of trivials and the major factor of success is how well you execute the one you choose; there are few significants, and the major factor in success is having them first/getting to market first. If you think you have one of the latter, NDAs might make sense.