Is poison use evil?

[Coidzor]

Like most people here, I say no - with the possible exception of poisons that explicitly cause intense pain or permanent physical deformities. But that shares a very blurry line with the "it's how you use it that determines its alignment" angle.
I can see the "it's dishonourable" angle, but I also see it as the weapon of the weak, of women (noncombatant, that is) and children.

Which brings us to the question, are there any that do that in D&D to your knowledge in the first place that you feel that caveat is necessary?

Think about it. You're an assassin - a living weapon. Your employers send you a picture, and you don't ask questions, you get out there and do it. That's what they want from you, none of this nonsensical "free will" and "thinking it over."

Which is quite a different picture from the scenario you first set us upon anyway.

What with it being "They tell you" rather than "You get to choose but can't actually choose"

It's not very clear, but the fluff of the Assassin class very clearly indicates that you aren't trying to be an Assassin, you're trying to be a member of the Assassin's Guild of Evil Murderers.

Which is probably is related to the whole annoyance at WOTC thing, yeah.

Though telling them to kill & replace the court wizard is a pretty lulzy way to get PCs perma-dead, I'll admit...