has there ever been a real attempt to support media diversity?

People can start media companies if they want. It so happens that most are liberal. The reason conservatives don't start their own media companies is that they don't think the public would like what they have to say.

Are you kidding? Look at the main stream media and see how racially representative of the national population it is. I think you'll find it's wildly 'diverse'.

so you want to change all that free speech stuff ?