Dear all, as an economics grad student in New York with a past at Munich University I feel compelled to contribute a few thoughts to the discussion- Do social sciences in general or gender studies in particular do or do not pay a good return to the investment made, and should the benefitors have to pay for their education because it doesn't benefit "the taxpayer"?
I am not going to babble about the value of studying social sciences and offering the possibility to study them for society as a whole - I believe this is pretty much undisputed. There's spillovers everywhere, and gender studies in particular has benefitted at least half of the population in uncountable ways. I want to make a few additional points.
In any given university there is cross-funding between the different disciplines. Physics, as long as no application pops up, is very expensive (labs & computers) but often has very little return on investment. Medicine, on the other hand, sometime funds a whole university, as seen at NYU where the patents on one single marketed product continue to pay of vast amounts of money for the whole university (but also bought the medical school the most lavish building on the whole campus, in the middle of New York City).
Many social sciences do not pay off much for the school it provides them, although in the US social sciences professors can make a lot as public speakers or (government) consultants (which may go in part to the university. In the same vein, over here for example a psychology lab may be donated by a former student or a corporate client of a particular professor, and donated to this professor in person, meaning (s)he brings the lab with him when hired at a university).
But social sciences are also on the cheap side; salaries are lower, there's no expensive labs or materials, relatively little computing power required, and their grad students are working hard in teaching for (longer) years and often have to return as adjunct faculty without secure jobs and little pay.
In the US, the undergraduate students who major in social sciences are in fact likely to heavily fund their peers in cost intensive subjects like chemistry, computer science, physics or medicine. In Germany, that's a little different - but even here, the social sciences often have the crappiest buildings, the oldest libraries and smallest offices (think TU München vs. LMU Politics).
What is more, Germany and the US have fundamentally different educational systems. In the US, everyone pays for their degree, including queer and gender studies. In Germany, the consensus was that higher education should be free and accessible to everyone, including the freedom to study a subject of their choice. This freedom and the joy taken from studying a "useless" subject can be seen as a value in themselves - and apparently have been seen as such in the past -, maybe even a value high enough to fully justify the investment absent any other benefits. Under governmental budget constraints this ideal has never quite come to be realized, and is further undermined now, but I personally believe our educational system contributes to the personal happiness of many people, and this alone makes it worth it.