My degree is in art education so let me clarify some things...
Most teachers aren't really trying to discourage the student's interest in cartooning ect., they're are promoting a broader scope of curriculum.
Any student with a specific esoteric interest or style receives similar treatment in terms of coaching them towards the broader classroom goals. There are student that ONLY want to draw one way or one thing...and that's a roadblock to even their own development as an artist. As an educator, you would be doing all students a disservice by only teaching them in their passions of the moment. One of my fondest moments, while student teaching, was mentoring a young lady away from her security blanket of only doing horse profile portraits. And in doing so, she also got better at her original love.
As a side note, there's a weird notion that any art style or movement that pushes boundaries is a case study of the legitimacy of all others. Minimalism, Cubism, Abstract or Dadaism are not meant to be shields against the traditional foundations of art...they're exploration of the limits of the form. As such, if I was teaching general anatomy to a class... The budding abstractionist isn't any different from the student insisting on Sailor Moon proportions. Both are off book.