While some might find this idea silly, you will never actually know if you might need it later on. Sure it's crazy to think that there is a whole society using magic coexisting with us, but in all honesty, we know just as much about what's happening in Area 51 as we are aware of Nargles or Threstrals existing in someplace where people have magic. (Yes, I am a Luna fan) So, this might not seem like a joke at all if somehow, someone, somewhere miss an 8th Horcrux, and we see He-who-must-not-be-name sending legions of Death Eaters at us.
People might find Defense Against the Dark Arts to be silly, but the most important part about an education is getting people to think about things and engage in discussion. Whatever gets kids talking when in class is important, and the idea for the educator is to introduce other issues while talking about something they can relate to.
It is very innovative of University of Virginia to offer Defense Against the Dark Arts in their computer science classes. The course attracts students due to their familiarity with the Harry Potter stories, and engages them in learning about computer viruses and computer security. It provides a vehicle for introducing students to computer technology, including programming and analysis. The university reports an increase in students entering computer science courses, which is attributed to this class.
In an era when students need more practical education, courses like this only serve as a joke. Ten or twenty years from now, it will not help them nearly as much as even a literature or art history course would have. Presumably, the students who sign up for it are hoping for an easy A to improve their grade point average.
Defense Against the Dark Arts is a fantasy fiction subject and does not exist in real life. Offering such class is like accepting some the fantasy fiction ideas to be real. This is not scientifically proven so does not need any official classes for kids to go to. As much as it sounds interesting, its not real and should not be offered.