Does the lecturer really need to be captured or cornered to deliver a Hannibal Lecture? Maybe it's Trope Decay, but I'm pretty sure I've seen a lot of examples that ignore this.

Fun example: the "Stupid! Stupid!" speech given by Eros, the "bad guy" (?) in Plan Nine From Outer Space. The gist of it is that human beings need to be dominated by a superior race because their history proves that they are inherently aggressive, and the arms race will inevitably culminate in the discovery and use of the Solaronite Bomb, a weapon so destructive it will start a chain reaction which will eventually blow up the entire Universe!

So his entire motive in trying to invade the Earth with an unstoppably awesome army of 3 zombies is to protect his own people, and all other sentient beings, from those irresponsible semi-evolved monkeys who don't know what they're doing.

The hero responds to this by taking offense at being called stupid and punching him in the face, which somehow sets fire to the flying saucer and eventually causes it to explode. Is this a happy ending, or did Eros maybe have a point?