At the Heart of the Abyss
Each race that can be considered for Spectre status has something they bring to the galaxy that no other race quite matches. While it’s true that almost all Spectres are from races that are heavily involved in the Citadel government, the Council does not overlook useful individuals on the basis of race. Ultimately Spectres are exceptional individuals who have shown themselves to be loyal to the Citadel government, and passionate about the preservation of galactic peace.
That being said, characters who come from non-Citadel races have not opened the door to Spectre status for their entire people, they represent a single, un-publicized exception to the rule. The choice of race for a character will affect that character’s statistics, and grant the use of a special racial power that springs from the unique gifts of that race. Each race also gets a number of minor bonuses, some of them non-combat in nature.
The Nemean Abyss is a dangerous place that does not recognize the Citadel Government’s authority in any way, so there are no real social benefits to playing one race over another. In the Abyss, everyone is treated equally badly, in a perverse sort of non-discrimination. At least, that holds true outside of the few systems that are held by Batarians, or space-faring races native to the Abyss. In general, however, there is no cohesive government or society to approve or disapprove of any particular alien type.