Angryfrommanchester, I am not being negative about Art! DH has a degree in Art; I certainly could not get a degree in Art as I am terrible at it.
The point is simply that some qualifications are considered to be more valuable than others, and young people need to be given good advice by schools on the likelihood of getting a particular job or going to a particular university if they take a certain range of GCSEs.
There are, in the eyes of employers, science qualifications that are less worthwhile and arts qualifications that are less worthwhile. It is not a case of arts vs. sciences.
But many of the fields where people are worrying about lack of social mobility are areas where state schools are not providing children with the opportunity to gain appropriate qualifications. Examples would be foreign languages, further maths and science subjects taught by qualified people.
There are many professions where it will be essential to have a qualification in, for example, Maths, Biology, a foreign language, or Art.
There are many jobs where you can get a job regardless of your degree subject - a Cultural studies or Maths student can end up as a graduate trainee at the BBC.
But it is extremely rare for someone to need a specific qualification in, for example, media studies or forensic science. In many cases, employers in forensic science would rather take a Biology graduate than a Forensic Science one for the tiny number of positions available anyway.
Schools, and for that matter universities, are not always very honest about these issues. If people want to do a course because it interests them - that is fantastic! I lecture in a subject area that rarely leads to a specific job. There are many degrees that make people generally attractive to employers without preparing them for a specific job - English for example.
I think that the problem comes when people believe that a degree in Media Studies or Forensic Science is vocational in the way that a Pharmacy or Dental degree is, when in fact MS and FS should be looked at as being more generally educational, and similar in purpose to an Anthropology degree.
In short, students should be aware of where qualifications are likely to lead them.