For some of the same reasons you might buy something from a local store instead of buying online - you can see actual faces in your community on the way, your library gets usage metrics that help it keep funding and stay around, you might be there already for something else, less time digging around in a screen ui and more time moving in 3d. I also like that the rip itself is totally offlime and not traceable. And it is just stressful wondering if something pirated has something nasty snuck in, however unlikely it is much less likely from a library dvd. Don't if you don't want to, but there are perfectly good reasons.