Rationality and intelligence are not the same thing - I've seen plenty of discussions here despairing about the existence of obviously-intelligent people, masters in their fields, who haven't decided to practice rationality. I also know people who are observably less intelligent than I am, who practice rationality about as well as I do. One major difference between people in that latter group, and people who are not practicing rationality, no matter what the irrational peoples' intelligence levels are, is that those people don't get offended when someone points out a flaw in their reasoning, just as I don't get offended when they, or even people who are not practicing rationality, point out a flaw in mine. People who are less intelligent will probably progress more slowly with rationality, as with any mental skill-set, but that's not under discussion here. The irrational unwillingness to accept criticism is.
Being called 'profoundly stupid' is not exactly a criticism of someone's reasoning. (Not that anybody was called that.) I think we're objecting to this because of how it'll offend people outside of the 'in group' anyway. Besides that, As much as we might wish we were immune to the emotional shock or glee at our thoughts and concepts being ridiculed or praised. I think it would be a rarity here to find someone who didn't. People socializing and exchanging ideas is a type of system -- It has to be understood and used effectively in order to produce the best results -- and calling, essentially, everybody who disagrees with you 'profoundly stupid' is not good social lubrication.
A currently existing social norm basically says that everyone has the right to an opinion on anything, no matter how little they happen to know about the subject.
But what if we had a social norm saying that by default, people do not have the right to an opinion on anything? To earn such a right, they ought to have familiarized themselves on the topic. The familiarization wouldn't necessarily have to be anything very deep, but on the topic of e.g. controversial political issues, they'd have to have read at least a few books' worth of material discussing the question (preferrably material from both sides of the political fence). In scientific questions where one needed more advanced knowledge, you ought to at least have studied the field somewhat. Extensive personal experience on a subject would also be a way to become qualified, even if you hadn't studied the issue academically.
The purpose of this would be to enforce epistemic hygiene. Conversations on things such as public policy are frequently overwhelmed by loud declarations of opinion from people who, quite honestly, don't know anything on the subject they have a strong opinion on. If we had in place a social norm demanding an adequate amount of background knowledge on the topic before anyone voiced an opinion they expected to be taken seriously, the signal/noise ratio might be somewhat improved. This kind of a social norm does seem to already be somewhat in place in many scientific communities, but it'd do good to spread it to the general public.
At the same time, there are several caveats. As I am myself a strong advocate on freedom of speech, I find it important to note that this must remain a *social* norm, not a government-advocated one or anything that is in any way codified into law. Also, the standards must not be set *too* high - even amateurs should be able to engage in the conversation, provided that they know at least the basics. Likewise, one must be careful that the principle isn't abused, with "you don't have a right to have an opinion on this" being a generic argument used to dismiss any opposing claims.