I would say that both diversity and quality are important and I know people like to say that diversity for diversity sake shouldn't be done but that's very easy to say when one is already represented in all forms of media.
Diversity for sake is okay. Everyone should be represented. The world isn't one shade, shape, gender or sexuality and fiction and the arts should reflect that.
When the odds /the playing field has been tilted in favour of one particular group for a considerable time all effort must be made to balance things out as soon as we can.