Thesis: Metal detectors should be implemented in high schools.
Antithesis: Metal detectors should not be implemented in high schools.

Vice-principal Johnson grabbed the knife-wielding student around the waist, then dodged as the angry young man flailed and tried to slash him. The knife nicked the administrator's arm. After the longest 30 seconds of Johnson's life, help arrived and the student was subdued. Another day in the intercity school.

At least this time no one was seriously injured. Mr. Johnson put a handkerchief on the cut arm to stop the blood flow. Incidents like this in our nation's schools are happening all too frequently, substantially hurting the learning atmosphere, and clearly show that metal detectors should be implemented in at-risk high schools.

OR

Vice-principal Johnson grabbed the knife-wielding student around the waist, then dodged as the angry young man flailed and tried to slash him. The knife nicked the administrator's arm. After the longest 30 seconds of Johnson's life, help arrived and the student was subdued. Another day in the intercity school.

At least this time no one was seriously injured. As Mr. Johnson put a handkerchief on the cut arm to stop the blood flow, he suddenly realized the spiral of violence that had occurred since the school started trying to crack down on violence by bringing in police officers and making threats to students. He realized that precious funding should be spent to solve the problem, not treat the symptom. Metal detectors would only add to the problem and should not be implemented in high schools.

Why Write This Kind of Lead

The psychology of argument dictates that people do not change their minds on an issue easily. It is best to find common ground, a harmless principle that both sides agree upon, before presenting a controversial thesis. If the reader then is favorably impressed with your attention getter, he will tolerate your thesis long enough to hear your arguments, especially if you begin those arguments with a concession to his point of view. There is no guarantee that the reader will be convinced, but he will likely hear you out, and that's all you can really ask, isn't it? Consider the effect on the opposed reader to beginning with a blunt thesis, such as: "Gun control is obviously a solution to all the violence in society today, and only poorly educated people oppose the idea." You're not likely to win many converts with that approach, are you?