I don't know if someone said this already, but probably because:
My name is Shepard Montoya.
You killed my father.
Prepare to die.
But in all seriousness, I'm open towards the batarians. My Shepard was a colonist, but I sort of like to think one batarian didn't feel right about the raid and helped Shepard escape, thus making Shepard not a racist towards batarians.
But still, for example in ME3, when Balak confronts Shepard and Shepard lets him go, I thought: 'aww, poor guy, lost his people and all.'
But Shepard said: I want you to shoot him, but let him go...
I was sorta shocked. I wouldn't of reacted like that and that was one of the moments where I thought they should've given us more dialogue selection.
I didn't play any ME DLC, so I don't really know their history together, but still...