There’s a literary tradition of making it be a choice, the romeo/juliet thing, and there’s a touch of it in many of the love stories in OUAT. Cora doesn’t want Regina and Daniel together. Belle’s father doesn’t understand about Rumpel. King George’s attitude toward Snow (or even Jack, though that wasn’t even love for James). There’s other examples though, as Ruth accepted Snow. Thomas’ family welcomed Cinderella in FTL (though they were against her in cursed SB).
Oooh, I like that observation. If they introduce Ariel and there’s a rivalry between mermaids and humans and Eric and Ariel are caught in the middle of it.