...kill non-feral ghouls? I've played a game for a while now and have yet to hear anything related to the BOS wanting to exterminate non-feral ghouls. While not everyone in the BOS likes ghouls, I've yet to hear anything relating to them wanting to kill non-ferals. In fact, all their comments about killing ghouls as always been referring to ferals. In fact, one terminal uses the words feral and ghoul interchangabley, so I'm wondering if those references people are hearing are in fact talking about feral ghouls.

I seriously want to know where people are getting this considering that's one of the most common criticisms I see for why people hate the BOS.

Yeah, I'm not sure. Maybe because sometimes characters will simply say "Ghoul" with no other context? Though, yeah, as you said, plenty of individuals are pretty vocal about their hatred for non-Ferals, yet you don't see or hear any being intentionally killed (though I wouldn't put it past any human being to kill one on their own out of pure spite). Danse calls Hancock a "filthy Ghoul" when you swap the two as companions, but that's all bark, no bite. At least the BoS members are on the same level when it comes to Ferals, Super Mutants, and Synths.

Interestingly enough, Preston is the first one you hear do this.

And why is it that nobody calls for the blood of the DC residents who apparently gleefully exiled all their ghoul neighbors?

I think it depends on the Brotherhood Knight. Some Brotherhood Knights would shoot a non-feral Ghoul if they could get away with it. They might even rationalize it by saying that "All Ghouls will eventually turn feral." Then there is the issue that Ghouls, Super Mutants, and Synths are all examples of man's hubris destroying civilization. Some might want to keep Ghouls around as a reminder while others might not want to be reminded that it can happen to them.

Is there actually any proof that the BOS knights would kill a non-feral ghoul like dialogue or random comments rather than just assumptions? The rest of the wasteland shares the BOS' dislike of ghouls so why is the BOS the only one that is criticized for it?