First of all, Steven Universe has a non-binary character, Stevonnie, who is human. There’s another non-binary character in Steven Universe Future, if I recall correctly. Since there’s both human and non-human non-binary characters, it’s not dehumanizing. Anyway, as a pan romantic asexual with an… interesting relationship with my gender, I don’t understand what’s so wrong with LGBT+characters not being human. The gems in particular are great representation because their alternate ideals of sex and gender aren’t treated as part of what makes them aliens. Ruby and Sapphire being a couple, for instance, isn’t treated the same as them not understanding the concept of birthdays, or not needing to eat or sleep. Also the creator of Steven Universe is non-binary and mostly goes by female pronouns, just like the gems she created! Some might chalk this up to internalized self-hatred, but it’s really just a different way of looking at yourself in relation to the rest of the world. Unless they’re otherwise grossly offensive, a non-binary character being non-human probably says nothing about how the creator views you as a person.