I'm interested in this question as well. To my mind, all educational institutions are meant to satisfy two objectives, the first -- and in my opinion the most important of which -- is to impart knowledge and cultivate a sense of intellectual curiosity; the second is to prepare students to enter society as knowledgeable, industrious, and productive members of the workforce. There is a strong correlation between the excellence of a university and the extent to which it succeeds in meeting each objective. Naturally, universities more successful than others in this regard are justified in charging higher rates of tuition than their less successful counterparts. (Graduate prospects -- as quantified by starting salaries, career satisfaction, capacity for postgraduate study [doctoral study, in this case], etc. would seem to reflect to reflect this.)
At the end of the day, education has (unfortunately) become a commodity; and the worth of a commodity to a consumer is judged, in large part, on its ability to meet and exceed the needs and desires of the consumer. In this case, students are the consumers; their needs are jobs and, more often than not, their desires are well paying jobs. LSE is widely perceived to offer its graduates excellent career prospects-- indeed, by some measures, the best of all universities in the U.K. Assuming that this is indeed the case (and in light of the foregoing analysis), LSE's tuition costs do not seem totally unjustified. I, like many students, wish they were lower, but as long as demand for places exceeds available supply (as it does each year in nearly every course) LSE has no rational basis other than charity upon which to lower the costs of tuition.
With that in mind, I don't think we can say that LSE is ripping off MSc students unless it is unable to fulfill its tacit pledge to afford them excellent job prospects upon graduation. The current state of the world economy has thrown its ability to do that into question. (See the original poster's reference to an alleged 50% jobless rate in the current MSc class in Finance and Economics, which, I think we can reasonably assume, generalizes throughout course offerings in nearly every field.) Without additional information -- such as that which recent graduates and students currently enrolled in MSc programs at LSE might provide about their ability to obtain jobs, let alone excellent ones -- I'm hesitant to say that LSE MSc students are being ripped off; but the fact that discussions such as these are even occurring does not augur well for LSE's continued ability to justify such high rates of tuition; neither, for that matter, does the fiscal state of higher education in Britain.
The fact that LSE MSc's costs are as high as they are is as much attributable to capped tuition rates on British undergraduates as it is to current market forces among seekers of postgraduate degrees. The dirty little (not so) secret fact of British higher education is that in order for universities to sustain themselves (i.e. pay faculty and staff, fund speakers, conduct research, etc.) and grow (i.e. do the things they must do to sustain themselves better), they must collect more revenue than that which is provided by undergraduate tuition fees. This is accomplished by charging international and/or graduate students two to three times as much in tuition as that which is paid by undergraduate students. Compared to, say, the U.S. educational system, this is essentially a "break even and grow at a snail's pace" business model. (This is why even the richest of U.K. universities -- LSE among them -- have absolutely pitiful endowments relative to even the most ordinary of private American universities.) From the universities perspective, such measures are essential to survival, necessary amidst market competition, and justified amidst market pressure; from the student's perspective, such measures are unfair yet understandable at best, and wholly unjustified at worst.
As someone from a country in which graduate study in the arts, sciences, and humanities is typically funded by the universities themselves (in large part, through undergraduate tuition), the situation in Britain is understandable, yet difficult to accept. With respect to LSE, the only thing that makes it acceptable -- at least to me, personally -- is the possibility that opportunities unavailable to me in the U.S. would be available to me as a graduate of LSE. Beyond the experience of living and studying abroad at a great university, these opportunities must inevitably translate into better job opportunities upon graduation. At the moment -- and probably through no fault of its own -- LSE's ability to provide those opportunities is in question; and, as a consequence, so too should most reasonable persons' commitment to attend the school as an MSc student, be.