Batman loses
“He wins because he’s Batman” is an exaggerated phrase. Bruce Wayne has spent an untold amount of time planning for everything (more on that in the next section). Because of this, Bruce doesn’t lose often. However, he doesn’t always win. Especially recently.
Having a hero who never loses is boring. This could be why DC Comics has had Bruce going through some of the darkest times of his life. In the last five years, he couldn’t protect Alfred, Gotham was taken over by Bane, Scarecrow, and Joker, he’s lost Wayne Manor, his hand (literally), and more. Nevertheless, these defeats will make his rise one of the most memorable. It’s also turned him into a more interesting character.
Batman was right to have a plan
In the JLA: Tower of Babel comic book and Justice League: Doom (the animated feature), Batman showed how prepared he really is. He has a contingency plan to defeat the Justice League. Bruce knows this because he’s studied his teammates and friends. The Justice League may have been offended, but it was the right thing to do.
As comic book fans have seen, heroes switch sides and fall victim to villains’ powers. For example, Superman has been mind-controlled by Maxwell Lord and Poison Ivy (twice). He also turned into a tyrant in Injustice. These are more than enough reasons for Bruce Wayne to be ready just in case.