I still think about him sometimes and wonder who he's bothering now.
Now, if you have a huge name and track record... I can get it. Years ago talked with someone who'd done some deals with the 'guerilla marketing' guy (Levinson IIRC). After a while, he was more or less just licensing his name/brand for a cut, but it was worth it because there was already a track record and built-in audience - anything with his name/brand would be guaranteed some degree of sales on day one.
Most people who've approached me with ideas like that haven't had that success. Even in one case where I was working with a guy who had executed multiple businesses and had good success (one 8 figure exit) - we just couldn't work together - our expectations of each other never synced up.
I've bothered to follow up on some of these businesses, and I've yet to miss anything substantial.
But in the absence of any other data, NDA becomes a very good indication of whether I should continue the conversation.
Can someone run off with an idea and make a billion dollars? Maybe. But I would suggest that an NDA gives very little protection. If the person is going to do that and actually manages to make a billion dollars from it, then all you have is a piece of paper saying the person won't discuss the idea without specifying the idea.
Unless you then have a paper trail of discussing the idea, how can you argue that that was your idea? Most subsequent discussions in my experience have been verbal.
Worse still they have a billion dollars to fight the matter in court.