The problem of tunnels that a centaur couldn't pass through as part of the story would be few and far between and the rest could simply be hand waved away by saying standard corridor is 8ft rather than 5ft. I guess I've rarely played a game where the difference in feet was threatening my suspension of disbelief and more than the guy inside a door swinging his two handed sword at me on the other side has.
Few and far between? It's
most multi-room human dwellings. Seriously, finding a bar in Prague that a Centaur
could get to the bathroom in is extremely difficult.
Finding a place to swing a two handed sword is one thing, but you're being confronted with a character who demands to swing a two handed sword not in
a place, but in literally every place she ever goes. Abstracting the fact that the character steps to the center of the room to swing a blade is fine, but if that character can't hold it up while going around corners or climbing stairs we have a problem.
The reason why dimensions so rarely come into play as a big deal is because D&D has already cut all the things that don't fit out of the system. Not only are Centaurs not playable in any meaningful sense in core, but pikes and other very long weapons don't even exist. There is literally no weapon in the game that you couldn't use in a narrow corridor with low ceilings. Weapons that couldn't be plausibly used in such a scenario just weren't even given stats.
And you didn't even fucking
notice, because it doesn't hurt the game that they are gone.
On the moral tangent: How to deal with the idea of poachers? Poachers in Africa are often shot and killed over killing "dumb" animals, even when they might be doing it solely to feed their families. How do we balance the these actions against humans in the moral matrix?
A world without gorillas is an uglier world. People fight, die, and kill to protect gorillas for the same reason that they would fight to protect an original Van Gogh. People will kill to preserve art, and fighting to preserve gorillas is no different.
Now personally I am not at all willing to write off gorillas and elephants as sapient. They certainly seem to have a sense of self and of play, and so on and so forth. And of course Gorillas are one of the very small number of non-human great apes left on the planet, meaning that in the long run the loss of gorillas would be a huge blow to comparative biology and thus to medicine, and thus have a real and tangible cost in human lives. And while those arguments are slam dunk in my opinion, they don't apply to everything. We don't protect tigers because they are top predator that keeps herbivore populations in check and thus ultimately preserves human lives by preventing cycles of boom and bust that spread famines and plagues. We protect tigers because we don't want to raise children in a world that doesn't have any tigers in it.
We fight and kill to protect tigers not because the life of a tiger means anything individually. We don't even do it because of the quite compelling ecological research that tells us that losing the tigers would end up screwing us more than is reasonable. We protect tigers because the world is beautiful and it has tigers in it. The world is beautiful in some small part
because it has tigers in it.
-Username17