Yeah sesame street had this problem with the "Snuffy's parents get a divorce" episode which the studio banned from ever being aired because they thought it would be too much for Kids with divorced parents. Or it might make kids worry that their parents arguing would mean they're going to get divorced.
I think they pushed the metaphor too hard when fusion was introduced, because the actual fusion characters are a fun idea and represent each characters relationship with each other. But our introduction to it was Amethyst shaking her ass.
Fusion can be a flexible metaphor but when you introduce it as an erotic act that's what it gets associated with for the rest of the show.
Avatar did this better with firebending, it has a negative and destructive connotation for nearly the entire run, both due to the villains using it and due to Aang burning Katara by accident.
But characters like Iron and the Aztec guys give us a deeper understanding of it over the course of the show, Steven Universe made the mistake of coming out the gate with sex. They should have introduced it as something innocent, because that's how we come to understand sex and relationships as we get older.