What are the disadvantages of having arts in the school curriculum?

Tough
question.  Honestly, I don't believe that there are any disadvantages to having art in a
curriculum.  I think it is an integral part of teaching the whole child.  

Unfortunately, not everybody feels the same way, which is shown by how many schools
have cut art programs from their curriculum.  I can lay out a few of those arguments for you.
 

One suggested disadvantage is that running a robust art program is
expensive.  There is some merit to this argument.  Art supplies cost more money that math
supplies.  Many people feel that money should be spent on "reading, writing, and
arithmetic."  Those are fairly cheap subjects to budget for.  

Additionally, schools right now are making big pushes toward STEM.  Science,
technology, engineering, and math.  Given the choice between paying for art or paying for STEM,
schools are choosing STEM, because that is the big push in education right now. 

Another possible disadvantage to running an art program is that art classes are
generally not required courses.  That means class sizes are likely smaller.  That's great for an
advantageous student/teacher ratio.  Unfortunately, budget wise, it looks like a teacher is
being paid equal amounts of money to teach fewer students.