Not sure if that's really a taboo, it's been commonly expressed on many Internet message boards, often self-referentially.
I suspect it's actually more that the average commenter on a forum related to their field tends to be more skilled than the average worker in that field, because the average worker spends their workday reading other forums that are unrelated to their field, but the very best professionals in a field are usually not found on Internet forums, because they're doing their job instead of talking about it.
Hmm, that's true. But I think message boards simultaneously tend to the "oh, I'm terrible, wasting time here haha." and to "Oh that guy's got so much karma, and I see him posting all the time. He probably knows what he's saying.".
I suspect it's actually more that the average commenter on a forum related to their field tends to be more skilled than the average worker in that field, because the average worker spends their workday reading other forums that are unrelated to their field, but the very best professionals in a field are usually not found on Internet forums, because they're doing their job instead of talking about it.