On the other hand, a spammer with a legendary account shouldn't be able to post there either.
Yeah, but they probably won't do that. I found a lot of the discussion in Ivory Tower to be above my head in a technical sense so I've had it and Serious Discussion on ignore for a while now. I don't think there's ever been a problem with higher-ranked members spamming either section, though I could be wrong.
I don't think Theymos wanted to have such a stringent requirement to post in IT or SD as an earned merits thing would be. He obviously realizes that most garbage comes from lower-ranked members (not all of them, of course). A merit requirement wouldn't be a horrible idea, but I think that would be too strict.
Given that the Ivory Tower is supposed to be a discussion board for serious senior members, I think it is sad that more eligible members don't contribute there. I did my bit to try to encourage its use, but I couldn't fight the sig famine there.
I'll have to un-ignore it and see what kind of discussion is happening these days. I have posted in IT before, but I didn't find it any more interesting than other sections, and some of the discussions died off rather quickly.
