I feel very lucky to have had a producer like Gene Roddenberry. He had a vision for the human future. Very optimistic utopian view. By the 21st century, he thought that we would have a much more enlightened society. The starship enterprise was a metaphor for starship earth and the strength of the starship lay in its diversity coming together and working in concert as a team. Visually, he wanted to get that infinite diversity and infinite combination philosophy visible by casting the way that he did.
Our colorism issues are horrible (the insecurity, the hyper-masculinity, men let alone not understanding the power of women, disrespecting women on a level that's just crazy to me, men becoming boys, not working as much as they should, not understanding the value of that, not understanding the value of a dollar, black people minimizing each other way before a white person does).