First, some background--I had the question come to me this morning while reading Cracked.com's "The 6 stupidest plots of supposedly smart movie villains". I'm a fan of Cracked.com's snarky tone in their posted lists, and this one made me sit back and think about the fact that I'd never considered the plot problems in most of these six cases, or others like them, quite the way the article did.
G'head, go read it. I'll still be here when you come back.
Now, were all six really the *ahem* most stupid (not "stupidest") plots out there? No, probably not. Were they stupid enough to deserve the article? Some of the commenters suggested no. I think, for the most part, yes.
One defender of the bad guys objected to the characterization of Inspector Javert as a villain. I can see the point; people can see Javert's point of view, can understand why he's torn to do what he does, can even to a certain point side with him. As such, he's kind of an anti-villain, which accounts for part of the endearing genius of the work. The Cracked writer would've done better to refer to him as antagonist rather than villain, then. And, to be fair, the original plot as contained in the book was a lot more complex than the scene that showed Wolverine saving the Gladiator. Regardless, I have to agree that in the situation as portrayed in the musical/movie, the comments in Cracked were spot-on. Why would a recognizable authority figure risk himself, and his side's plan, with personal intervention rather than sending a more junior, less recognizable person?
Several of the other examples were instances of the same flaw, one that doesn't necessarily manifest to you while you're engrossed in the story. Then again, if brilliant villains don't think about "Hey, what do I do with all this money/land/status once I destroy the system that makes it valuable" why should we? The stories were fun to watch, anyway, right?
That leads, then, to the first (technically, #6) flawed plan: that of Hans Gruber in Die Hard. Here, again, I have to side with the Cracked writer over the commenters, and I have to admit that some of the technical flaws occurred to me while I was watching the show, too. I have to further admit that the movie has always struck me as a true Bruce Willis masterpiece--a parody within an action movie, one where the brilliant villain is actually a dumbass.
Yet the commenters take the article to task--if Hans Gruber is brilliant, they reason, then he's probably holding his true plan close to his chest all the way till his plummeting death, right? Okay, that's possible, but it takes my idea that the movie is a brilliantly-done parody of the genius bad guy and smashes it against the wall of poorly-told stories. Please, please don't do that to me. See, we all expect antagonists (and, sometimes, protagonists) to hold parts of their plans in reserve, hidden away from the knowledge of all of their fellow characters. That said, we, the story consumers, are not characters. An author/screenwriter who holds his an/pro-tagonist's clever twist back to the very end before revealing it to the readers/watchers is brilliant. Hiding some of the plot through the entirety of the story and past the words "The End," though, is just dumb storytelling.
There's also the pro-Hans argument that he really did plan all of that, and it might've worked, but that the idea of leaving evidence behind was a function of his arrogance as a brilliant criminal mastermind. Sure, and the idea of leaving a garbage chute on the south side of your great big planet-killing space orb open to a single torpedo isn't dumb, either, because it's.... No, wait, it really is dumb. Brilliant villains are allowed a certain amount of arrogance, but when the arrogance becomes a flaw in their plan, it turns into stupid.
I'll give the commenters this, though--the principal in Ferris Bueller's Day Off isn't meant to be a smart movie villain. Anybody who goes into that movie expecting to see anything other than a farcical caper of stupidity is probably going to leave crying. Ragging on that movie for stupidity in the plot is like ragging on, say, Toy Story for too much animation.
All that said, though, as a guy who crafts plots, it's good to be reminded once again that it doesn't take a perfect plot to be a commercial success.