It's about getting the right balance. Having said that i will give slightly more weight to interest in the area of study over demands by the job market. Why? Because i value the opportunity to get educated in something i am interested in as much as a job opportunity. But let's be pragmatic: interest is just one part of the puzzle. I am interested in cooking and baking, that doesn't make a great cook and doesn't remotely guarantee that i will succeed as a chef or baker. If i did really badly in first few years in law school i will immediately review my choice.

Being interested in the study also doesn't mean interest in the practice. With the legal market so unattractive now, i admit i am contemplating a career switch ( wait i don't think i even established a legal career) ... so that's another point for prospective students and students of law to ponder.