Should the demographics of our characters reflect those of the fictional universe in which they live?
In traditional roleplaying, this mattered very little, as the population of player characters stays very small in proportion to that of the universe as a whole. A gamemaster easily compensates for a party of 4-6 PCs by ensuring that the overall population reflects the expectations and flavor of that setting.
But in MMORPGs, most of the universe with whom the player base interacts will actually consist of other players. NPCs certainly populate the world, but beyond quests and any other PvE content, they’ll play a very small role. Among “hardcore” roleplayers, problems frequently crop up here. One player makes a choice that others perceive as being an “uncommon” one, perhaps because in the fictional universe as a whole, very few of that sort of being actually exist (e.g. a Lethan Twi’lek).
But should that really matter? For the most part, PCs are much more adventurous characters than your average inhabitant of the setting, so it stands to reason that something being uncommon overall doesn’t mean it need be uncommon among players. Whether or not a player intends for an “epic” or “heroic” feel, generally the character has much more opportunity for adventure, travel, and ability than other denizens.
Of course, further roleplay should reflect the choices made thus far. The very characteristics that make these characters stand out inevitably affect the reactions they engender in others. So research the lore appropriately, write the character background in such a way to reflect an understanding of what that rarity means, and play the character in an informed manner. This might mean conforming to the stereotype, but it might just as well mean rejecting the stereotype and playing with an awareness of the character’s disposition towards it.
Don’t take it too far, though. Characters shouldn’t fit a demographic so rare that virtually none exist, even in free-form RP. Generally, very rare types have some imbalancing feature that would make playing one tantamount to godmoding. While all players certainly get to decide for themselves what they want to do with their time IG, antagonizing other players via poor RP etiquette won’t lead to nearly as much fun as some might think.
So when creating your next character, don’t think too much about whether or not very many exist in the universe. Think more about whether the character will interest you and, just as importantly, whether the character will interest others. That will lead to much more enjoyable interactions.