Batman was right to make the contingency plans. Batman was also right to not tell anyone about the contingency plans.

Imagine you're a member of the Justice League. Now, imagine you turn evil. What would step one of your evil plan be? Did you say "do everything you can to keep turning evil a secret from Batman and try to get the drop on him to take him out first"? If not, you are bad at evil plans. After all, you know he has a contingency plan for you. You know his track record for these plans is very, very good. He's the biggest threat by virtue of this. Sure, he's just a man dressed up like a bat, but he's very smart and very crafty. The Flash could easily find enough kryptonite to make an entire suit out of the stuff and beat the crap out of Superman, Wonder Woman and Superman are pretty much physical equals, there's very little that can truly be done about Plastic Man, Martian Manhunter can literally go intangible or tangible at will and can fist your brain, most of these people are fighting on a very equal level and if one of them has killing intent when the other doesn't, the one down to kill will likely win.

Batman on the other hand? All you need to do is hit him before he has a chance to react and he's done. He's just a man dressed up like a bat. If Wonder Woman, Superman, or Flash slam into him at full speed, he's getting the A-Train treatment. Plastic Man has seen enough tentacle hentai to know where this is going. Martian Manhunter can just fist his brain. The Atom can go dance a jig on his neurons via a phone line and then pull an Ant-Man vs Thanos's butthole to Batman's skull. People always talk about Batman always winning via prep time, but the corollary is Batman always losing without prep time. Because he is a man dressed up like a bat.

Now, imagine if you didn't know about Batman's contingency plans. What's step one going to be of your evil plan, believing that Batman has no plan for this? It's going to be to deal with Superman, Wonder Woman, Martian Manhunter, and Flash. They're cracked out as hell. They're the heaviest hitters on the team. They're the biggest threat to you around.

And then Batman pops out of the shadows and takes you out because he had a contingency plan and you weren't paying attention to the man dressed up like a bat. You gave him prep time because you didn't think he mattered. You didn't know he already planned for this, you made him aware it was time to use it, and he got the drop on you. Now you're screwed. Evil arc over, Batman wins, flawless victory.

That's why Batman keeping the plans secret was the logical maneuver. The only reason any of his contingency plans are any good is because he has the element of surprise on his side. As soon as you know that he has the contingency plans, you are going to plan around his plans. You are going to make sure that he doesn't know it's time for the contingency plan until it's too late. He's going to be the first person you target if you know about the contingency plans, so unless you went evil in full view of the world, you are going to win this thing. The contingency plans are worthless without being secret because anyone with two brain cells to rub together is going to realize they need to kill him first once they're aware of the contingency plans.

And having them? Yeah, that just makes sense. The superheroes of the Justice League have a near-perfect win rate against a boatload of supervillains. Many of them are the most powerful beings on the planet. If one of them goes evil, it's much worse than a normal supervillain. They're actually competent. Depending on what kind of evil, this could be very bad very fast. Imagine The Flash bloodlusted carrying a knife. He could stab a whole city to death in the span of a sneeze. In an hour, he could eliminate almost all human life on Earth. Frankly, everyone is very lucky that the Reverse-Flash has never thought of making Barry live with being the last man on Earth. He could do that.

Superman could crack the planet. Wonder Woman could crack the planet. Martian Manhunter could do a ton of damage just via exploiting shapeshifting. Green Lantern could blow up the planet. Aquaman can flood the planet. These are end of the world level threats. Sure, some of them aren't such an issue. Oh no, Oliver Queen is going on a mass shooting with arrows. That's like, not even as bad as your average day in America. Nobody's worried too much about Green Arrow turning evil. But a lot of them are.

So yeah, having a plan for that? Logical. And making sure they don't know to kill Batman first if they want to win? Also logical. The only way they ignore Batman is if they don't know about the plans. If you tell them the plans, the first step of their plan is to kill Batman before he knows to use his plan.