[quote=@Raxacoricofallapatorius]
To further expand on the assumption that the species [i]are[/i] individual species: in a setting where there is the possibility of half-breed characters to occur, those half-breeds would likely be treated very badly (for semi-viable reasons) by their respective societies, even though being a half breed is of course not their fault. It kinda brings a new weight to the trope of half-breeds being taboo but not otherwise suffering any actual genetic disadvantage. 
[/quote]

I wonder if that's intentional - using the fantasy "races" to explore real world race conflicts and problems (interracial marriage, stereotypes, etc.)