I strongly suggest you use switch side debating as an advanced game or lesson or whatever. It's incredibly helpful. Choose a topic that there won't be prior opinions on, like the actions of a fictional dictator from history against an external threat, or something. Putting people into small teams as opposed to making them debate individually would be best, I think.

So you make them debate the topic on one day. Then the next day, you make them debate it again. Except on that day, they argue for the other side of the topic. I suggest using multiple small teams and having a series of short debates so that all teams face each other round robin style. Give a small reward to whatever team gets the best overall record.

You'll need judges for this.

This is a great way to make people rethink positions that they've grown close to.