To have non-hostile Goblins there, you need to have pacified them before entering their territory and you break your previous decision/behavior by attacking them afterwards despite them not being aggressive toward you. Not a very honest or merciful of you.
No arguments about this part ...
I just cant help the feeling that if you pick a side, promise to help, you do help, and THEN you attack anyway ... its not much different.

And I had the impression they changed the roast to not be a Dwarf in a previous patch?
Dont know anything about it ... but Goblin in blue tousers keep talking about a Dwarf they killed and are cooking ... and there on the roast certainly still is Roasted Dwarf Leg, and Belly ... you just cant eat it anymore.

For the Karlach vs Anders, it depends how you do it, what your character knows in-game and the conversation you had with both side before killing either.
I believe i described that quite thoroughly. O_o