These are meant to be scary, cautionary tales to keep Bronze Age peons from asking difficult questions of their betters. To say that they have outlived their usefulness is wrong, since they were never useful to begin with. At some level, though, we've all imbibed them and they can be invoked in rhetoric to elicit certain predictable responses. By and large, these ensure to the benefit of those who have acquired lots of knowledge. You might not think so, for the Promethean myth is ostensibly a knock on academics. Not so ostensibly, though, it gives scientists a reason to put on priestly airs and, by hinting at the perhaps no-so-priestly stances of their counterparts in other countries, haul down defense grants. And it gives non-scientists an implicit pitchfork to brandish in the scientists' faces. Accordingly, a kind of deal has been struck in which both scientists and non-scientists have ended up accepting the Promethean myth as being a passable model of reality. Call this the Promethean consensus. The Promethean consensus is something that no one would ever admit to believing in, if you pinned them down and tried to get them to engage in that level of introspection, but is universally hammed home by every movie and TV show about science and a good many books as well, and obviously underlies the public postures that scientists are expected to adopt.Stephenson goes on to talk about how various academic cultures treat each other, making a distinction between prestigious coastal universities and what he calls the Midwest American College Town (or MACT). I don't know either culture well enough to comment, beyond saying that I found his theories interesting.
Once you've bought into it, the only two stances you can really take toward the Promethean consensus are to respect its rules or to willfully break them. You are either a priest or a bad boy. Priest because, if you are one of the keepers of the academic flame and are willing to allow that some of your knowledge is dangerous, you can get a lot of mileage out of intoning the right solemn and portentous sound bites. Bad boy because the downside of the Promethean myth has largely gone away. No one is getting expelled from the Garden of Eden or being chained to a rock to have his liver torn by vultures anymore. it's true that modern-day scientists have to take their share of flak, but, with the exception of people who run girls' schools in Afghanistan, or the occasional biomed researcher who's run afoul of the animal-rights activists, they no longer have to dodge pitchforks. And so if you're one of the people who actually has access to Promethean-grade knowledge, there's no longer much personal risk, and so, to the extent that the knowledge is perceived as dangerous, it can just feel kind of cool, in a naughty way, like you're a teenager who just figured out where Dad hides the keys to his gun cabinet.
Do we still use the Promethean myth today? We do have large amounts of gate-keeping when it comes to science and academia. Unorthodox theories won't fly unless the theorist has strong credentials. Some of this is no doubt useful just in terms of controlling the flood of information but also no doubt some important things get dismissed out of hand unfairly. But this doesn't feel connected to Prometheus.
As Stephenson points out, modern scientists and academics don't face too much risk for bringing forth advances or theories. In fact, it's the exact opposite. If Scientist X thinks he has something, there are more avenues than ever for getting that something out to the public. How often do you see news reports about some theory that is due to be printed in a scientific journal? All the time. And if that 'something' doesn't pan out? The scientist's career will still be fine, especially if the 'something' got lots of publicity.
I don't think that we still have things that 'shouldn't be known by man'. This is undoubtedly a good thing.