This is one of the funniest jokes in American humor. One of the most witty, insightful, ridiculous, and absurd passages in American humor, equivalent to the writings of Mark Twain or Kurt Vonnegut, and it is buried deep in a video game parody done in flash thousands of pages into a webcomic. The joke is hilarious, but convoluted.

First off, Homestuck is a webcomic where we meet an alien race called Trolls, humanoid insects that live on a brutally violent planet, with a weird society and a weirder biology. Our human protagonists meet the Trolls and form alliances with them, because underneath their brutal exteriors their culture is much more complex. Oh, and also, The Trolls are each modeled after a different sign of the Zodiac. There are twelve of them, with their personality somehow based on their Zodiac sign, although not in a conventional way. One of them, who we meet thousands of pages into the story, is Karkat Vantas, a foul mouthed and physically weak troll who is still taken by the trolls to be their leader. Despite being a mutant.

This takes over a year of real time writing to get to.

We then find that Karkat Vantas is the Second Coming. In his own society, his "ancestor" was the equivalent of Jesus, who was executed for questioning the homicidal blood caste system of Troll society. So we have a character, and another character behind him. We are then given the revelation that all of this alien history comes from the second iteration of reality, and that there was an original iteration behind that.

So three years later, we, the readers, along with the characters, including Karkat Vantas, meet Kankri Vantas, the version of Jesus that was raised in a non-violent, utopian culture.

I am a couple of paragraphs into this, right? Well, for the readers, they had to wait three years to get to this point, where we meet Kankri Vantas in a weird dreamscape. So what is Jesus like, raised in a utopian society? Taking away the fact that he is a cancer-themed alien, this is the real question we have. And in a section that takes place in a parody of a 16-bit video game, we talk to Kankri. And he is a snide, pretentious, self-righteous, jargon-spewing, condescending and generally insufferable teenager. With no real oppression to struggle against, he launches a multipage lecture to Karkat (and the reader) about the nature of identity and social struggle. Replete with hashtags. And trigger warnings. Another character states that he is:

"assiduously deconstructing every conceivable, hypothetical form of injustice no matter how obscure, except those that I happen to think are kind of important?"
While the jargon that he spews sounds somewhat like what would have been current on tumblr in 2012, it all takes place in him criticizing the alien world he comes from, with a very different alien biology, and a very different form of sexuality, than we are used to. And, since he is themed around the sign of cancer, he writes every "b" as a "6" and ever "o" as a "9", leading to the reader having to read several pages of this:
I'm saying, and we can take a 6rief time-9ut while y9u summ9n y9ur m9irail t9 help pacify y9u, assuming y9u have 9ne. N9t that I'm presuming y9u d9, 6ut I heard that y9u did, is that c9rrect? If n9t, I ap9l9gize. I further ap9l9gize if y9ur 9rientati9n precludes the p9ssi6ility, as a pale ar9mantic, panquadrant demir9mantic, s9mething in the gray palesexual department 9r such, and h9pefully y9u are n9t triggered 6y such presumptu9us c9ncillian9rmative language.
By the time you have read several thousands of pages into Homestuck, this just seems like part of the joke. That alternative-history, Cancer-themed alien Jesus was giving us a wall of text full of weird characters was just part of it at this time. In the right mindset, it is a hilarious and insightful piece of prose.

But here is the real joke: this came out in 2012. At the time this was written, the tumblr SJW was already enough of a cliche that the intended audience got the joke automatically. There were smug, self-righteous people on tumblr, who ignored real problems so that they could be self-superior. That is something that the internet cognoscenti already acknowledged and knew as a thing a decade ago, and we could laugh at it. So the real joke is that ten years after this was made, ten years after the joke was a mainstream joke, there are parts of the American public who still think that "someone on the internet might be judgmental" is a new and insightful comment to make. We have real problems, but people will ignore those to focus on a point that was already encapsulated perfectly on the internet a decade ago.