If 'widening participation' ends up meaning working class children can only study STEM courses, and only the children of the rich study the arts and humanities, that's an impoverished view of social mobility, and of (equal) human flourishing https://twitter.com/charlesforsdick/status/1388408082020057095
Given the role of the arts, and history in particular, in shaping our national identity, in determining what stories and narratives get memorialised and subsidised by public funds, there is also a significant democratic, public argument against this social class narrowing
We can't be surprised about the relatively middle class preponderance not just in who visits museums, galleries, theatres but who works there, what the content is, if we simply nod along to the view that working class kids must study STEM in the name 'social mobility'
Of COURSE some/many people gain more in terms of human welfare and flourishing, not just £, in studying STEM subjects. That is good for them, and for social mobility. What is NOT good is streaming working class kids out of arts and humanities in the name of 'social mobility'