So...all humans are the same?!?!?
Sure. You seem to be set on the idea that all dragonborn are culturally the same, or whatever. Why not all humans? This is all chosen; fiction is creationist. Why
choose humans to have diverse cultures, while forbidding them to any other species?
I'm not convinced that non-human characters are anything other than humans who look like non-humans with some mechanical bonuses.
Because...that's what they are? Dead serious. They're sapient beings--all of them. That means they're all capable of good and evil, they all belong to a culture and an origin, they all had childhoods and challenges growing up, etc. You admit to presuming that non-humans will necessarily be over-the-top stereotypes, all cut from the same cloth, but why can't they have cultures that cut
across species lines? Arkhosia, for example, was the "Dragonborn" empire in 4e--but it had many human, dwarf, elf, etc. citizens as well. That's unavoidable with an imperial culture.
A dragonborn druid devoted to the Green Faith should have far more in common with a human druid dedicated to the Green Faith than she does with a dragonborn paladin of Bahamut. The first two actually
share a culture. Why should having scales, or breathing fire, completely rewrite a being's potential for culture until it
must be genuinely alien? It's not like they don't value the same things (they build empires, do trade, study magic, raise children, worship, eat food, etc., etc. ad nauseam). It's not like orcs are axiomatically more interested in wearing furs and hunting mammoths than they are selling silks and counting coin.
Uh...okay...all the fluff you include in your responses makes it difficult for me to figure out the point you are trying to make. I think you are trying to make a point about how humans can be good or evil. I do this too, I just don't need Dragon People or Cat People to accomplish that. As for the otherworldly horrors and such, well I use monsters in my games, and not all of them are evil with a capital E, though most monsters are there to antagonize the PCs.
My point is that EVERYONE can be good or evil. Instead of "it's Humans Only Club" for the good/encultured guys or "it's (what you call) Monsters Only Club" for the bad/non-cultured guys, it's...just people. Dragon-people and hairless-ape-people and bird-people and green-and-tusked-people. And there may be some humans who far more strongly identify with an orc, because they're both tribal nomads, than they would with other humans who are city-dwellers. Or whatever.
What's so special about humans that they actually develop distinct cultures? Why do only humans have cultures that can cross physiological lines, while non-humans are definitionally locked into one and only one culture because of their physiology?