Is poison use evil?

[Coidzor]

Those are two different scenarios by design. The former is after you succeed at joining the assassins, the latter is while you're trying to qualify.

Do you have a response to the conundrum I posted after that?

Other than that you're not beholden to the assassins at all after you take your first level of the PrC, so the fluff is out of whack if the only guaranteed assassination opportunity is cheapened and played as just straight up stabbing some random guy in the face.

As for the conundrum you posted, I've gotta run out the door, but skimming it, the "for no other litmus" is failed in the second case because you killed them because it was easier to justify as an entry killing to get into the assassins. Which is similar to failing because "I chose him because he's prominent and it'd be more impressive/flashy to actually succeed in killing a batman wizard than some random barmaid."