Thanks to Arthur’s subway killings, and the rhetoric used by Thomas Wayne, there are many Gothamites who use clown disguises to take part in anti-social behavior, and it very much inspires a wave of class warfare.
And in a way, it does.
There is no questioning that Arthur Fleck goes through a transformative experience, and part of that transformation is wearing clown makeup and committing to a murderous lifestyle – but he’s noticeably not the only one who makes that kind of a leap.
As he becomes Joker, Arthur is held up as a leader of the movement, particularly after the televised murder of Murray Franklin, but one could imagine that while he becomes a figurehead, he’s not necessarily the one and only who, years in the future, will go up against Batman.