Man, this case is a bit of a mess in what different points have been brought up that all ideally should get addressed.
Right. Let's begin.
1) The case for Rule 4. I start with this because I think this is the weakest case. Certainly, the appellant's rhetoric that that thread has been very much over the top and, may I say, warbling - all the name-drops of philosophers, the invocations of higher but ultimately irrelevant philosophical principles, the sheer unnecessary wordiness. I would say that is suboptimal, as it does project an attitude of rubbing one's sophistication into people's faces, which can be a problem. But I wouldn't say it is infractable, and in terms of precedent we have always let preaching from on high stand, if no specific rules have been violated. In that context, even the rhetorical exaggerations of the appellant like "Hitler particles" are... yeah, suboptimal but IMO not infractable.
2) The case for Rule 2. Is calling for the destruction of all art hateful in the terms of Rule 2? Well, there are several points to that:
-I think calling for the destruction of all figurative art is, as the appellant has done, is per se just a statistically very out there statement. In such cases, we must take heed that we do not just penalize an unpopular opinion. But, at least bare the other considerations that will follow, I do not think it is should be infractible just for being so out there. We have had other weird statements come up in tribunals, and generally only actioned them if they are bigotted (which requires a specific group to be targetted) or run afoul of the Rule 4 maxim of being extra careful about sensitive topics (which I think the appellant has been - one can hardly accuse him of not having been detailed with his replies, for example).
-There is the "Internet Tough Guy" angle of Rule 2, of course, but I don't think that applies here at all. That angle is meant to exclude edgelords, but I don't think the appellant was being edgy - it's not like he led with this opinion/attude, and he didn't push it into people's faces. It took the back and forth of a discussion to come up, and even then it was just some lines in very long posts. Therefore, I think it is fair to describe that as a genuinely held belief that genuinely came up in the context of a discussion - rather than general edginess.
-There are those parts where the appellant called specifically for the destruction of conservative art. Now I absolutely do think there should be no instance of "acceptable targets" on SV, and everyone deserves the same baseline of respectful behaviour on the forum. However, as a category, "conservatives" are not a protected group on SV in the same vein that cultures, religions or ethnicities are. And certainly, calls to curtail free speech have a long tradition on SV that reaches back to its very foundation. I do not think precedent would support action here.
-One thing where the call for the destruction of art may be of relevance, though, is the issue of cultural erasure. Of course, yes, the appellant has been pretty universalist in the application of his opinion. At one point he said all figurative art is to be destroyed. So it certainly is not directed against any one culture or group of cultures in specific. However, regardless, it would in fact result in the cultural eradication of groups of people, even if that is just a "side-effect" - but a pretty obvious and central side-effect.
That I do see as a problem, because ethnic and cultural identities, and hence culture as an identity marker, are protected categories on SV. So yeah in t hat one particular aspect it may be a problem, but I am willing to hear counter-arguments to that.
3) The case for Rule 3. This is something the Arbitrator raised, even if they ended up labeling it as "Rule 2 and 4". But regardless of classification, the case is still there. There are no "acceptable targets" on SV, so calling a group of people "morons" whose "psychological anguish" is "sublime pleasure" is a problem. And unlike the calls to curtail conservative art, this one is targetted not at their ideology, but at the people themselves.
...on the other hand, reducing this whole thing to just some people being called morons, when that quite obviously is not the meat of the argument, that would sit a bit wrong with me... hmmm...