In the Gotham City of 2019's Joker, Arthur is an aspiring comedian, working menial jobs, while relying on the city's failing social services for a neurological disorder that causes him to laugh uncontrollably in a city where this is less and less likely to happen organically; crime and unrest is on the rise, people are losing their jobs (Arthur and his social worker, included), no healthcare for the ill (Arthur's mother), while the city's elite terrorize the city on their way back to lavish suburban estates.
One night after losing his job as a party clown, after his self-defensive weapon falls out of his pants while entertaining children at a hospital, and the coworker who gives it to him for self-defense lies about where it came from, Arthur is attacked by employees of Wayne Enterprises, who are harassing a woman until they set their sights on the laughing Arthur. He kills two in self-defense, and while a third is fleeing, kills him as well. Thomas Wayne, a billionaire and scion who functionally runs the city and is now seeking to do so as mayor, decries this violence as the work of "clowns", something which inspires many to protest in constume in solidarity with (anonymously) Arthur.
Wayne, however, is who Arthur is led to believe is his father; his mother was once a Wayne Manor employee, and alleges that she and Wayne had an affair, and now she needs Wayne's help at the end of her, now, painful and ailing life. Arthur approaches him multiple times, and Wayne denies this, while dismissing Arthur and, more broadly, the class he represents in his dismissal of Arthur's claims. Meanwhile, Arthur, in his disordered state, is held up as a village idiot, by neighbors in the community, tolerated as a token at work, regarded as little more than novelty by Murray (a talkshow host played by Robert De Niro; many parallels and homage sexist between this film and Scorsese's King of Comedy, where De Niro's Rupert Pupkin plays a similar role to Arthur's relative to the role he plays here– if you've seen this, then this aspect of the story won't be unfamiliar to you when Arthur appears on Murray's show as unrest finally boils over and breaks out in Gotham). Amidst all this violence, the public seems to be wondering why Wayne and his ilk aren't asking why now, why violence, before rebuking the legitimacy of the frustrations, and that's what solidifies what, until then, is characterized only by intra-working class tension and conflict, into solidarity against Wayne and the city's elites.
Arthur's social worker says, "They don't give a shit about people like you, Arthur. And, they really don't really give a shit about people like me either."– the system is engineered to manage an improverish class of exploitable cog-class of people, with functionaries to manage those they deem the defective pieces, and what happens when that latter class of exploitable people becomes a sizeable cohort, those who were tasked with rehabilitating them and keeping them working are reclassified failures, and the goal posts of who matters in a society move to exclude more and more people, shifting the social burden away from others into narrow and narrower scopes, where the only thing one can afford to care about is keeping a job that, to come back to the beginning, doesn't "give a shit about you", but you need to literally survive. This is the Marxian reality of the universe of Joker; it's a fascist hellscape using artificial and engineered scarcity to marginalize everyone but the ultra-wealthy into subsistence, and it's the ineveitability of revolution that Wayne, in this case, seems to be concerned about most. He dismisses anyone cheering the anonymous Arthur as "clowns", only to find himself protested, wished the worst, by these clowns.
Arthur, in confronting Wayne, who he still believes is his father, he implies there's something lost in human nature to reject a child, or an overture in good faith from a child, to kneejerk react by believing the worst of their intentions (believing Arthur is after money, not acknowledgement of where he comes from– he's told he's adopted). Whether or not Arthur is Wayne's son is immaterial to whether or not he's right, just like the reasons for Arthur's actions after being attacked are immaterial to the mass outrage and organization it sparked, these are genuine, and observable human responses to suffering and discompassion by an unfeeling society. This Gotham depicted is a society that is well summarized by Marx's dictum "The bourgeoisie cannot exist without constantly revolutionizing the instruments of production, and thereby the relations of production, and with them the whole relations of society." driving Arthur, and everyone else in the film, to the margins to find solutions to problems this society is equipped, but unwilling, to solve outside of token personal charity and the orderliness of bureaucratic incrementalism while everything gets demonstrably worse in the interim, almost as if it's not working at all!
The film ends with what is Batman's well-known origin story; a random murder of his parents, sparing young Bruce, and he becomes a vigilante crusader for justice. What this film does differently is reimagine this dynamic, and puts into perspective of the film's established narrative that while the Wayne's were enjoying the theater, riots by the desperate and the ill-cared for were exploding across the city, inspired by one man abandoned by not only the city built by Wayne's elite class, but by Wayne personally, as well. It takes little imagination and only a passing familiarity with the Batman origin story, and a lifetime of living in the imperial core, to understand how these murders would be framed only one way by the mass media, and how the rioters, protestors, Arthur himself, his actions and motivations, can only be framed another, but in the end, completely in conflict with one another, or else face admitting failure of the bourgeois, neoliberal economic order's role in killing the working class, and driving it to the brink, only to fall on deaf ears and (implied in the reference it makes to the origin story) receive a demand for compassion for one's oppressors in return. The cycle perpetuates once more.