Have you ever come up with what appeared (to you) to be a knock-down argument for your position; but only after it was too late to use it in whatever discussion prompted the thought? Have you ever carried that argument around in the back of your skull, just waiting for the topic to come up again so you can deploy your secret weapon?

I have. Hypothesis: At least some of the landmines you describe stem from engaging someone on a subject where they still have such arguments on their mental stack, waiting not for confirmation or refutation but just for an opportunity to use them.