My issue with kill all tieflings attitude is related to the rules of this world as I understand them (and as very patient forum users explained them to me). If we know that in FR there are inherently good and inherently evil beings, but there are those that aren't (like the php races that could have any alignment). If you arbitrarily decide that because X percentage of tieflings are evil all tieflings are evil, why not apply this logic to all other races that are not inherently good?
I'm sure the answer to this is pretty obvious. Let's say that 99% of all drow everywhere are baby-eating murderous bastards who would kill you for the sheer fun of it. And then let's say 60% of all gnomes are standoffish isolationist who just want to stay out of your way and leave you alone.
No-one would equivocate between killing a drow and a gnome on first sight under these circumstances. At that point, killing a drow on first sight is either self-defense or a favor to the realms, while gnomes just leave everyone alone and for the most part they don't hurt anyone even though 40% of them might be up to no good. The point is not about moral perfection, the point is about some races being dangerous and actively harmful to everyone else. If you can kill a 100 drow with only one of them being someone who isn't explicitly evil, can anyone justifiably blame you for prejudice, when statistically speaking, your prejudice makes the world a better place? I mean, most places in the realms are not going to be nice to orcs, because orcs are primitive savages who will murder and rape for fun (hence half-orcs).
Add to that the fact that in the Forgotten realms you can just worship a God who is okay with this kind of behaviour and you get yourself an afterlife that is not Hell. Case in point: Kagha I mean who is going to blame someone in the Forgotten Realms for dedicating their lives to the elimination of goblins, drow or orcs? And why should he care about other people's judgement? There is an elven deity whose portfolio is exterminating the drow (unless they removed him).
