Without that practice these assignments may well be undoable. It quenches the desire for knowledge and the love of the truth. This is clear from the fact that killers of whites are much more likely to be sentenced to death than killers of blacks. Yet blacks are six times more likely to be murder victims than whites are. We should not build more nuclear power plants in the United States.
More accidents are likely in the future.
It is selfish and unfair to use a technology which benefits the present at the expense of future generations. The op-ed section in the newspaper is a good place to look, but you may use any argument you find anywhere. You will find something if you keep looking. Keep in mind that the more carefully written the passage you are diagramming, the easier it will be to diagram. But clarity of argumentation is not the same as shortness.