I get your point. But i think you poorly named your topic.
1) If you are going to kill everyone, what stops you from doing it after you asked all questions? Removing the need for the spell.
2) "Speak with dead" isn't Larians invention. It is a DnD 5e spell. And it is one of those that are hard to implement good (hence the advertisement).
3) Noone is forcing you to abuse this exploit to get all the XP in the game. I finished DOS2 without using it.