Back in August, Warner Brothers announced that Todd Phillips was going to direct a Joker origin film, starring Joaquin Phoenix. Just a couple of days ago, they announced that Jared Leto would be starring in his own solo Joker film.
I didn't think one Joker standalone film was a good idea, let alone two.
Firstly, I do not believe that the Joker needs an origin. While I know that certain comics have given our favorite villain an origin story. Most commonly, he is a petty thief known as Red Hood who falls into a vat of chemicals when being chased by Batman. Most of the origin stories end up changing throughout the course of the comics, or end up being changed.
DC is attempting to create a film universe in the same vein of Marvel's Cinematic Universe, and so far it seems that the Joaquin Phoenix movie is the Joker's origin story. Solidifying an origin story for the Joker robs him of his mystery; part of what makes him so terrifying is that he is an unpredictable villain. By establishing a known origin for him, it rids him of that quality. It also may become too sympathetic, making the Joker into more of an empathetic character than he is supposed to be.
Second. The Joker has had stand alone graphic novels before. However, I do not think a stand alone movie will do justice to his character. Part of what makes the Joker such a fantastic villain are his interactions with the protagonist. There is no word yet on whether or not Batman will be appearing in these films, but I simply am hesitant on the idea of whether or not Joker could hold an entire two hour movie by himself. Perhaps I will be surprised, but I'm not sure that the film will have an interesting dynamic without the rivalry between the Clown Prince of Crime and the Caped Crusader.
Another point I would like to make: I don't think that a mainstream audience would be interested in either Joker movie. Most of the fans clamoring for a Joker film are hardcore comics fans, and while I respect that, I do not think it is something that would transition well to a mainstream audience. The Joker is a character that has been in comics since 1940. There are a lot of texts and character building in the comics that a mainstream film audience simply does not have. A cinematic universe cannot build such a complex understanding of a character in such a short amount of time. The comics have had 78 years to build these characters and it isn't something that a movie universe has enough time to do, especially as it seems that DC is trying to catch up with Marvel.
Lastly, while I do think that movies with protagonists who are terrible people can be fascinating (eg: Pulp Fiction, The Social Network, Whiplash, etc.), if the Joker is given his own movie, it would take away the horrific villainy of the Joker, and instead replace it with too much sympathy, or even pity. Origins often create a reason for a character to do something, and once someone like the Joker is given a reason, he becomes sympathetic. The moment he becomes sympathetic, he loses part of his appeal. Half the fun of the Joker is not knowing what he is going to do, simply because he is so insane. Once he is given a reason for acting the way he does, it explains all of his actions and makes him predictable.
The Joker does not need to be given a standalone film. It would rip off his mystery, his dynamic with his hero, and it would rid the audience of the fun of watching a villain simply being a villain.