Personally I like to base it on Racial Tension in the 1900's USA. And your view on the scarpping of Racism lacks precedence and plausibility no offence, for example, The United states, founded as an Immigrant nation mean't for everyone for Freedom and shit, is often rated as one of the most racist places on Earth, despite having one of the largest populations of Foreign descent. Yes maybe Human Racism would eliminated, however we Humans love to hate, and considering the Tajarran and Unathi's in superiority it is a sheer wonder why Humanity has not Enslaved them or made them into Client states. Sure we can bring up the alliance of the Skrell, but we must remmeber in any case the original alliance was for pragmatics.