Should have been rejected or edited to remove the bloviating parts in the beginning? Hard to tell - moderating is not easy...
If this guy is known/regular in ASUG a behind the scene direct message at the beginning may have placated some of it. This may have removed interpretation of skill levels and 'insults' or potentially on the defensive. If the behaviour continued without an audience then lock or remove thread.
You are right - moderating is not easy. It's subjective and sometimes you give a little to see what direction a thread takes and then regret it. If someone with RFC expertise has time, a blog explaining the risk with high level examples (or possibly one exploit with the comment on how to prevent this) and then remove the thread. I do feel a bit bad that the thread remains there for the life of SCN's time with some of the comments. At the same time, that thread now has a lot of useful information.
I find it someone has to call themselves an expert of skilled then they may have a higher opinion of themselves compared to others. Experts/Skilled people do not tell everyone how knowledgeable they are unless it's a job interview. And even then, it's usually demonstrated and implied.
For this one, I would edit the comments that are personal attacks/assumptions and stick to topic only or remove it altogether.