jlb524 wrote...
And Erinya is depicted as an irrational xenophobe...
...and Ashley would be a... rational xenophobe?

Mind you, I don't confuse xenophobia with racism as some poster seem to do. Being distrustful of/intimidated by other cultures is "only human". Effort is always required to open up to cross-cultural exchange and I certainly wouldn't blame a turian for looking out for his own people before charging to Earth to fight the Reapers in ME3...
But concerning Xilizhra's OP: Yes, I agree that the writers likely made up Nef's story to portray Morinth as a monster; by monster, I mean a person that preys on people as if they were food; like a beast but without the excuse of lacking self-awareness... Reapers fall pretty much in the same category, considering how insignificant individual lives are to them. Granted, Reapers do it on a massive scale... and it's easy to treat a million deaths as a mere statistic. Does the fact that Morinth killed/fed on only hundreds make her less of a monster? Does her own perspective on these killings make them less amoral?
Had Nef been an impressionable
male artist, the message would have been less powerful. Furthermore, Nef's mother's anguish was clearly intended to echo with Samara's own, as she is doomed to lose her own daughter as well. So yes, Nef's story is "contrived" to illustrate the writer's intent as to Morinth's nature: a monster. And it is the task of the Hero to fight Monsters. To force the Hero to kill a Monster who happens to be her Child is the stuff of classic tragedy.
I am saddened by Morinth and Samara's tragic fates, but I don't sympathize with Morinth. She is a victim of her A-Y condition and whatever choices she made when she ran, but it desn't excuse or ennoble her victims' death. She was intended as an antagonist in Samara's larger tale.