[Logophile]

But many student groups believe that using a service like Turnitin is too punitive and automatically presumes guilt.

Their reasoning is faulty on two counts. First, punitive means "inflicting punishment." Turnitin is a an investigative tool; it does not punish anyone. Second, simply checking papers for plagiarism does not presume anything except that some people will cheat (15% according to the article).

And that is the point. Some people will cheat, and these "student groups" want them to get away with it. If they were honest, they would admit their real motivation. But of course, if they were honest, they would not be working to aid plagiarists.

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Fifteen percent is the number of students that are caught. I'd bet an index finger that the number of total students who copy and don't cite sources is much higher.