I've done this type of thing quite deliberately. It's not hard to figure out.
If you want kids to write about and/or debate on one or both sides of an issue, then you can demonstrate both sides of an unassigned issue as an example. Here's one I used:
Illegal immigrants should not be refused medical help or education in California.
That's clearly very controversial -- how would you demonstrate to students ways to present both the pros and the cons for this issue.
If parents want to pay for private education for their children, no one will object.
That's not controversial. How would the presentation of pros and cons differ from the first topic I gave you?
The main thing I think, in controversial subjects, is to make the students realize there are differing points of view, and the teacher has to stay neutral and let the students defend sides. Examples above are good.
Should ninth graders be allowed to drive cars to school?
Should driving on the school campus require maintaining specific GPA?
Now on noncontroversial topics, it is not as necessary for the teacher to stay neutral.
In teaching world history, it's important for students to understand the differences and similarities between major religions.
The teacher can carefully and without bias present this information.
These are this year's and next year's National debate topics.
Policy Debate 2008-2009 Topic
Resolved: The United States federal government should substantially increase alternative energy incentives in the United States.
Resolved: The United States federal government should substantially increase social services for persons living in poverty in the United States.
One way to work in class is to divide the class in half, use class time for the halves to work together. Then after a week to schedule a debate, let one group of four debate for 10 min, then switch in another group of 4. After the hour, then let the whole class by secret ballot vote on which side presented the best argument. The next week, then we would spend at least one day analyzing the arguments that had been presented, and whether they were valid or falacious. The students enjoyed the process.