Quote Originally Posted by Mnemnosyne View Post
Even going by the ristupulous rules you're quoting, that only theoretically makes it ok to kill a fiend if they are or have been on the Prime Material for a significant enough time to fall under that rule on page 35.

Otherwise, killing a fiend simply because it is a fiend falls under murder, because the justifications that excuse killing evil creatures under the description of Murder as an evil act on page 7 explicitly depend upon 'because it still stops the creature's predations upon the innocent.'

Therefore, killing a fiend on any plane other than the Prime Material without having individual evidence that this particular fiend is actually committing evil is murder. Even killing a fiend on the Prime Material may be murder, if the fiend has not been on the prime material for a significant enough time to cause lasting harm as per page 35 of BoVD. Even if you claim killing one is a good act, it's still murder and therefore also always evil.

Furthermore, none of this actually depends on the fiend being of any alignment other than its natural alignment. A fiend could theoretically be evil due to its beliefs, but never actually do anything evil, and therefore killing it would still always fall under murder, because killing it cannot be excused by stopping its predations, since it wasn't doing any predations.
See the thing is, just by existing they are preying on the innocent. Furthermore, the BoVD defines murder as a killing of an intelligent creature for a nefarious purpose. If a paladin has a nefarious purpose for killing anything they probably should have fallen long before the issue of whether or not killing fiends is evil comes into play.