Imagine this: You're a team leader and frustrated because the office kitchen is a mess, and not for the first time.
Do you say, 'Too many people are leaving the kitchen in a mess. Please tidy up before you leave ' or 'Thanks to those who tidy up after using the kitchen'?
It works the same way as inoculation delivered in a syringe.
You give your audience a small dose of the opposition's argument to stimulate their defences.