As a substitute teacher, I have taught several sessions in the library. I have been teaching research skills to third through sixth graders. A consistent theme is the problem of plagiarism.
As a writer, I want students to respect the work of others. People put time, money, and effort into their words and images just to have them used by others without credit or pay. I have credibility with students when I share that I blog and have had my work used without attribution.
Turning in someone else's work as your own is cheating. Using their art without paying is stealing. This could be copying words and images from a website, watching pirated videos, or downloading "free" games from an illegal source.
When I tell them that I have had people use my writing and art without giving me credit, they want me to sue. I explain that usually I send an email to the offender and that takes care of it. (I'm sure it's happened other times, I just haven't caught it.)
As a teacher, I have a responsibility to set a good example. When I plan my lessons, I need to use legitimate sources. I need to know what constitutes fair use and stay will within the limits.
Fines are expensive. Your reputation is priceless.