You know, I was pondering things a little while ago about heroes and villains and something struck me; the reason the villain ends up being defeated because they talk about their "evil" plan is not because they are dumb or stupid, its because they just want recognition. I mean, look at the villains, most people can relate to them more than they can relate to the hero. The hero saves the day, the hero is who people want to be, but the villain is who people can see themselves in. Villains don't start that way, they are not born evil, they are born as innocents who are then mistreated by the world. It is just like us as average humans, we are born and we live in a life where we are constantly being misunderstood and disregarded for our efforts and used by those around us. The natural desire of human kind is to be loved and cared for and noticed, but that doesn't happen. Villains are representatives of this notion and this flaw in humanity, they become "evil" because they have this overwhelming desire to be noticed by someone and to do something that gets noticed, that they can take the credit for. Really, they are just trying to be loved and understood and recognized - just like we are every single day. So when a villain stops in that moment when he has the hero cornered and the end is surely in sight, he isn't being stupid or dumb in describing his "evil" plan - he is only trying to get recognition and praise, he wants to take credit for this thing that he has done. In this situation the hero is the parent or the teacher or the coach or the captain or the friend who takes that moment to listen to what we've done and then turns around and steals it all away. The villain isn't defeated because he is stupid, he is defeated because of his overwhelming need to be able to tell someone what he has done and be proud of it, something that we desire to do everyday. This common scene is a direct representation of the, arguably, biggest flaw in humanity: the desire for recognition that will never come except for in fleeting circumstances where it is then ignored.
So, I don't think villains are all that bad or unintelligent - they are just like us, a fact that I think many people ignore. Think about it, who do you have more in common with? The hero or the villain? My bet would be the villain.