It might stem from pre-existing viewpoints on other nomadic peoples, like Gypsies, who have reputations for being thieves and kidnappers.
As for the Boer war type, that sounds like something that we'd find in the early days of the Alliance colonizing planets, running into Batarians once or twice when both colonized the same one. I'd prefer Turians, but they'd have little interest in colonizing a levo world, as we would a dextro. Such planets would be traded to other sides for economic and political benefit, or strip mined for useful resources and abandoned.