With Star Trek, it means that someone thinks that people like you have a place in the future. One where you are valued and treated as an equal. Some of us don’t have that in the present. We live with fear and uncertainty because certain political parties decided to make our existence and rights are a political issue and up for debate. That may not mean much to some people, but they know they have nothing to fear. Their future isn’t in doubt and at the whim of politicians and religious hate groups.It's fine if you don't "need" it, but the audience in their millions probably includes people who do. Representation is about more than dragging the lumpen populace by the nose to certain conclusions, it's about giving voice to people who haven't had opportunities to use the megaphone of popular media. I don't "need" Star Trek to inculcate me in the notion that LGBT people can have meaningful relationships, but if I were a gay teenager and my particular corner of the world didn't have a lot of out gay people who could serve as examples, the relationship between Stamets and Culber could give a powerful message about the possibilities open to me that I might not be getting from my teachers, my peers, or my parents.
When I see the majority complaining about diversity, I just see a glutton complaining about a starving person asking for a bite.