And that's MY problem: the idea that there is something you can instantly tell about a person just because you know where they're from. The bumpy forehead in that case is just a proxy for any random racial/cultural sigil that identifies you as whatever-it-is-you-are, and then you are expected to look, talk, act and think a certain way or else you're not a "true Klingon" or "true Ferengi" because you don't fit the stereotype.
In fact, if you replace the species names in any of the dialog in TNG or DS9 with real ethnicities, the problem becomes pretty apparent:
QUARK: Listen, do you hear that?
BASHIR: I don't hear a thing.
QUARK: Exactly. The ambient noise level in this room is less than thirty decibels. On an average day it's sixty five. When there're Mexicans in the room, it can go as high as eighty-five.
O'BRIEN: So what you're saying is, it's quiet in here.
QUARK: Too quiet. Something is terribly wrong.
BASHIR: Like what?
QUARK: I don't know. But have you ever met a quiet Mexican before? Look how they're watching the room. It's like they're picking out targets. Where are you going?
O'BRIEN: I thought I'd ask the Mexicans what they're up to.
QUARK: Don't do that.
O'BRIEN: Why not?
QUARK: I don't want them to know we're on to them.
Or when Worf DIRECTLY calls out Martok's wife for being the racist old hag that she clearly is:
WORF: You never told me that your wife was opposed to this marriage.
MARTOK: Sirella is a woman of strong convictions. She believes that by bringing aliens into our families we risk losing our identity as Klingons.
WORF: That is a prejudiced, xenophobic view.
MARTOK: We are Klingons, Worf. We don't embrace other cultures, we conquer them.
IOW Martok's answer is: "So what?"
Star Trek too often hangs a lampshade on that kind of issue without actually dealing with it, so the Klingons -- more than almost anyone else -- come off as caricatures rather than fleshed-out characters. Martok and Worf are the only two who break the mold, and they only ever manage to do this by expanding OUTSIDE the parameters of "Warrior guys who love to fight."
All that really means is "Warrior guys who love to fight" doesn't actually tell you anything useful about anyone, so it's useless as a defining characteristic of the Klingons. It doesn't tell you how their economy works, how their language evolved, or anything about their music or culture. It doesn't tell you anything about their responses to pain or pleasure and, in the end, any attempt to extrapolate those things from that single characteristic wind up being silly and one-dimensional, and trying to keep that one-dimensional concept in frame is just an exercise in racist thought.
Hence my point: the defining characteristic of a Klingon Warrior is the
Warrior part, not the Klingon. Since just about anybody can be a warrior, trying to reduce the Klingons AS A SPECIES to that is an artistic self-immolation Star Trek is better off avoiding in the future.
Or a black person who doesn't listen to rap, or a Mexican who isn't lazy...
Which is a BAD thing.
Because strictly speaking, any individual person is unique in some ways and typical in others. It's the combination of expected and unexpected traits that gives you a fully fleshed-out character. If the only time you add variation is for some kind of plot twist, you're pretty much undoing any world-building that MIGHT have resulted from that variation: Klingons who don't want to shoot everything are just anomalies and freaks, everyone knows True Klingons are just grumpy bikers who drink alot.
The most important thing about human nature is that humans are DYNAMIC. No two people think exactly alike, make the same choices, come from the same place or meet the same end. No two people have exactly the same perspective on what is right or wrong, and that is the source of most of our conflicts in life. How two different people struggle to make sense of the exact same event is a major characteristic of the human condition, and the choice to either seek common ground or force one viewpoint to submit unilaterally.
But the moment you start using species/race as a proxy for those viewpoints, you're already on a path to completely miss the point. Mainly because of the opportunity for common ground: you miss out on the opportunity to tell a story about the Klingon dancer who ran way from home because the local shaman (who, with 20 villagers, is chasing her across the galaxy with a bird of prey) think she's a reincarnated goddess (which, in fairness, she actually IS) and want to put her in charge of the entire county. You miss out on that story about the Ferengi mathematician who offers the theory that the only reason the Ferengi as a species are so obsessed with profit is because they're really just obsessed with MATH and they like to count things (might as well be money) and he spends the entire episode proving that you can describe just about anything, no matter how complex, if you have enough numbers. You miss out on the opportunity to show a Borg ship wander aimlessly right through the Bajor system, scan DS9, scan Bajor, scare the hell out of literally everyone, and then as it turns to leave the system, turn suddenly and attack/assimilate a shuttlecraft flown by a war criminal and then leave (turns out this particular cube had been sent here specifically because the Collective wanted to understand the concept of "Remorse").
You can't tell stories about races of people. You can only tell stories about individuals. The species your character belongs to can help you frame the background, but when you try to flatten the topography of the world you're building, that background becomes a lot less useful to successive characters.
