Joker was popular because it resonated with people who feel like they've been kicked in the dick by Society. It shows a man who is mistreated by his job, his family, and the people who just live in the city. People can relate with feeling small, being humiliated by spiteful assholes, or feeling like they just don't belong in general.
It provided catharsis to people who sympathized with Arthur because, even though what he did was wrong, he chose to no longer be a victim. He decided to fight back against the people who made his life a living Hell.
The reason why people hate Joker 2 is because it was solely made to spit in the face of people who sympathized with Arthur. The reason why Arthur gets raped and killed is to demean Arthur, who was a symbol of someone who rejected a Society that alienated and abused him. Hollywood, the "System" in general, wanted to destroy that. The movie serves as a warning to people who disobey the system.
