I'm mixed and am against the term "Half" being used as a societal reference to a marginalized group. This means "Half-elf" (specifically as a societal label or rules object) feels off to me. An individual can call themselves "Half" all they want (that doesn't bother me, and it doesn't make you racist for wanting to identify that way), but that is a personal choice. Being called "Half-something" should not be forced on all mixed folk as a societal label, or in a game rulebook.
Also, regarding the Origins UA Mixed Species argument, the "One Drop Rule" accusation is inapplicable. It's not even a good metaphor. You don't have to like the rule, but don't misprepresent it with real world racist accusations. The One Drop Rule said if you had one drop of something, you are only that thing. That is not what is happening. If a character was born of an Elf and a Half-elf parent, they are going to have the stats of either an Elf or a Half-elf, not a mix of both. It's not racist to say the player has to pick one Species to represent their Species Abilities. Using that same logic, it's not racist for the child of an Elf and Human to have the species abilities of one of the parents. It is the same player choice for if the parents were an Elf and a Half-elf (unless the DM limited it further, like in Eberron.)
One could argue that Eberron's take on Khoravar half-elves is more problematic because in Eberron, all Half-elves breed true, erasing their human and elven origins. But we need to stop going down both those rabbit holes.
Species abilities are not the sole representation of a character. Their cosmetic portrayal, cultural origins and story, and having the species "tag", all matter. Using the Origins document, sibling "half-elves" (even twins) don't have to have the same species abilities. They can each take after a different parent, and be diverse both mechanically and visually. Heck, they can even be paternal twins that look identical but have different species abilities based on their parentage. There is no erasure. The player is the one getting to choose how the character presents mechanically and visually. The player has the same options as everyone else, but their appearance and background can be more diverse/unique. That's even more freedom.