The following contains spoilers for Deadpool 2.
There's a lot that Deadpool 2 does that is quite different from what we're used to seeing in traditional superhero movies. One of those things is the movie's lack of a traditional bad guy. The film has multiple characters who could be viewed as the antagonist, but none is the comic book villain that we're used to seeing our heroes battle on the big screen. Of course, Deadpool is never afraid to subvert a trope for comic effect, but in this case, the decision to not have a standard bad guy came simply from the fact that they didn't need one, as all the characters they had were already going to conflict with each other. As screenwriter Rhett Reese says...
We decided we had enough people with differing motives butting heads that we didn't really need a traditional mustache-twirling villain. We had the evil headmaster, we had Juggernaut, we had Firefist himself as an adult in the future, we had Cable --- and sometimes Deadpool is his own worst enemy in some ways. So we thought, 'Why feel trapped into the trope of a villain who wants to conquer the world? Why not just have the particular goals of these characters come into conflict?'
The primary conflict in the film comes from Cable, who wants to take down Firefist as a boy before he grows into the man who kills Cable's family. Neither of them is necessarily a villain in that case. Firefist is a child has yet to do anything wrong, but Cable's motivations are understandable and are far from evil. The headmaster of the orphanage where Firefist has grown up is truly evil, and Juggernaut is an unapologetic bad buy too, but neither of them is really a main character, the former is simply a motivator for Firefist, and the latter acts as a bad influence, but little more.
Nobody here is looking for world domination or ultimate power, they just have things they want, and those desires collide with the desires of others, leading to the film's conflict. Deadpool just wants to keep a kid alive, but also wants to stop him from doing something terrible. As co-writer Paul Wernick tells the L.A. Times, the lack of a traditional villain makes the film more challenging to create, especially since Deadpool 2 is dealing with some real emotion, made extra challenging by the movie's focus on humor.
As a filmmaker, I loved the challenge of not having a conventional villain. As you start to peel the onion back, you realize the real villain is all of us because we're not showing [Russell] the compassion that he needs. That's the big idea in a movie full of crazy action and fart jokes, but it felt right and earnest. The first film was a love story and this movie needed a real genuine emotional hook.
We know that early versions of the Deadpool 2 script included a larger role for the X-Men villain Black Tom Cassidy, but in the end, it was decided that he simply wasn't needed to make the movie work.
Deadpool breaks the superhero movie mold every chance it gets and this is just one more place where that happens. Overall, it clearly works.