You completely misunderstood the post.
Yes, it's a lazy insult, but 'lazy insults' are not incompatible with self-moderation. "lazy" discourse is essentially inherent to this sort of platform, and it becomes more prevalent the more active it becomes. On some ideal imageboard everyone would exclusively contribute only sparkling & cogent posts, but we don't exist on in that universe. We have to live with "laziness" being an perpetual factor. My contention is that "lazy insults" can and have positive utility on 4chan as long as the thing being insulted is deserving of being suppressed or discouraged and the insult effectively creates a hostile environment for it.
"Pleb", I think, was a "good" insult for 4chan because it carried with it an implication of failing to meet a higher standard of expectation among posters, which is GOOD. 4chan SHOULD hold itself to a higher standard and "pleb v patrician" reinforces that. Just the awareness in the back of a posters mind that he might err in being "pleb" creates an incentive for higher content.
Too much attention is given to the superficial and obvious of posts actually made instead of why other posts are NOT made. Posters don't just 'decide' to make a good post. There has to be a place that fit to receive or encourage them. I think boards are kind of like an 'ecosystem' that, when they are healthy & working properly, includes "lazy insults". Maybe, like an ecosystem, if you try to get rid of one part because you think it's bad, it upsets the whole thing or gets replaced by something even worse.