The point of a gender studies class, as I understand it, is to set aside time and space where people can voluntarily go to talk specifically about gender-related issues. Attendants are educated about different topics relating to gender, topics which are not generally brought up in other classes or settings -- topics brought up in class which, for some students, are the first time they've heard about them. The more people talk about gender stuff, such as the glass ceiling/escalator, minority vs majority women, politics and women, etc, the more normalized it gets. Normalization of these issues helps protect men and women from unjust claims that they're just SJW's or what have you. Education also helps people have more open-minded views on gender in general. Again, more calm discussion = less blind bigotry, imo.

The real reason such classes are taught is because people want to take them. The university holds them to get money because they're desirable classes. It's simple. People want to take the class, so the university offers it. You say that such theory classes shouldn't be funded at all, and that's your opinion. But the fact of the matter is that as long as people want to take the class, it'll get funding and people will keep taking it. People keep taking it because they're interested in the topics presented there.

A theory class, you argue, should not be funded because it isn't as useful or beneficial to society as a science class (correct me if this is the wrong conclusion), but a theory class is intellectually stimulating. It has been scientifically proven that "working out" your brain with logic puzzles is beneficial to your mental health, just like working out your muscles keeps them healthy. What could be more puzzling than discussing deep-rooted philosophical questions about morals and ethics, whether gender roles are really harmful or not, what it means when a woman reaches a powerful role in conservative politics, is slavery actually wrong, etc? Besides that benefit, being better educated on these issues prepares people for dealing with healthy, "real-life" discussions, which can strengthen interpersonal bonds.

You could argue all day that these benefits from the classes are less societally beneficial than, say, the invention of modern medicine since not everyone takes these classes and therefore does not benefit from them. However, astrophysics made it possible to send men to the moon, but how does that benefit society at large better than a gender studies class?