If it were simply a matter of being told, I could have just told myself, since I've made that argument myself on HN for years. But the point was to try the idea for a little while and see what happened. Now we have actual experience to point to.
HN is large enough that if the outcome had been wildly different, other users would be thinking that had been obvious all along, and telling us so.
Keep in mind that the important question was how the community would react, and complex social systems aren't straightforwardly predictable. I've been working with HN for years now, and a participant for years before that, and much of it remains counterintuitive to me.
There's still the "should I really stick this knife in that electrical socket?" evaluation that should take place with weird/crazy ideas, though.
This experiment was like asking people to flag "news", and getting surprised that people were flagging tech news, when they really wanted to avoid crime news.