Against Elf and Dwarf
Trolls from Glorantha, one of the few demihumans I do genuinely like.
One of my more polemic opinions on TRPGs is my general distaste for what those familiar with D&D call "demihumans" - the elf, the dwarf, the hobbit (undignifiedly referred to as "halfling"), and so on. My issue with them is, in part, aesthetics; I do not like how they look and behave, and the post could end here to be honest with you. Some folks enjoy having a full category of PC that speaks in a bad Scottish accent, drinks a lot, has hair-trigger temper, is a stonemason or some other sort of guilded craftsman, and looks like they might enjoy heavy metal if it existed in Grim Fantasy Land where he comes from, and that is fine.
However, another part of my dislike is that these things are additive, not assumed, and I just don't see what is to be gained by adding them to my game, especially considering humans are quite weird enough, and people have a lot of thoughts on that. From where I'm sitting, I see two types of demihuman: the painted guys and the rara avis.
The painted guys are like Star Trek aliens, they're humans in all ways that matter but they have prosthetics to look different and have a little gimmick about them. They usually live in their own ethnostates, have a stout racial identity, and their racism is a lighthearted joke for the table to pretend like they have something against "knife-ears". My problem with these is self-evident - if I wanted funny guys I could just make guys which are funny, I don't need a category of Funny Guy, who lives in Funny Clans over on Funny Kingdom, all of which are biologically predetermined to be funny.
Many gamers, however, consider it bad form for your elves to be just dudes with pointy ears that measure their lives in centuries, and that's where they bring in their beautiful rara avis. They proclaim to the four winds that the correct way for these magical creatures to hold weight is for them to operate in a completely different fashion than humans. I've been in so many conversations with so many people who elaborate on how exactly their elf-variant is actually very fun because they snuffle goop and don't live that long, or their dwarfs are sculpted from stone given life and that shapes how they see life, or their goblins are actually insectoids, etc.
My problem with them is this: they're never that weird. People bend themselves out of shape trying, insisting, pleading for their demihumans to be different and unique, to engender in their players a completely different view of the world that they would get from a human, but they can never be meaningfully strange and inhuman in the actual game - the thing that matters. In the lore, on the pages of the rulebook or the lines of the blogpost, they can be however you like, but the fact of the matter is that this must always be filtered through a thought-process which a human would be able to understand, because it is a human playing it. Therefore, all demihumans are painted people to some degree.
Some people might protest this saying, for instance, that one can play a character which is much smarter than them, or holds much different beliefs from their own, and so on. The issue there is that "being intelligent" is still within the realm of possibilities for a human, the thing the character is striving to be is a more perfect human being but a human being regardless, whereas the thing that the special demihuman is striving to be is not human - it is like trying to create a perfect flashlight that emits light the same colour as no light at all.
What these people chase is the feeling of what Tolkien called Faerie, the realm of magic where strange things live and operate, and which mortal men may only access through enchantment. The process through which these "Elves But Different" are made is often one of defamiliarization, attempting to seek the strange within the familiar and reframe one's view of these classical tropes through it. The reason I argue it doesn't work is that this process has to be undone for it to be concrete; as soon as the player writes "Elf" on her character sheet and brings it to the game, she is guiding her character through thinking in human terms, because she has to, that is the only way any of us has ever been taught to think, and any thought-pattern we might have is a human thought-pattern.
From where I see it there is but one solution, which I think will be unwelcome to all who ponder these matters: a player can never play as a thing which is meant to be genuinely inhuman. Faerie cannot be truly known. The Game Master might have his own human thoughts on how his inhuman beings act, but the players aren't privy to them, much like how the GM describes a hurricane through his best approximation of what it understands its behaviour to be like, focused on the product of its actions upon the world, not on the internal cosmovision of the hurricane.
I believe this will be a unwelcome solution because most TTRPG players chafe under the concept of unavailability and limitation, but I believe that, for the inhuman to remain inhuman, it cannot be translated in a way that a player can feel safe in portraying that character. The moment the player feels confident in how a fairy ought to feel is the moment it is dragged from beyond the veil to the fields we know and subjected to the light of rational thought; it is by understanding and categorising that magic dies.