So here's the net effects on our diplomatic situation if we go with the Siren trade:
Current Views of Avernus, as per end of Turn 92:
Asgard 18/10
Alfheim 8/10
Vanaheim 9/10
Jotunheim 10/10
Midgard 12/10
Svartalfheim 8/10
Niflheim 8/10
Muspelheim 11/10
Byzantium 8/10
Results if we convince Garp (chance that Sigurd will side with opposition):
Asgard 18/10
Alfheim 5/10
Vanaheim 6/10
Jotunheim 6/10
Midgard 9/10
Svartalfheim 5/10
Niflheim 8/10
Muspelheim 11/10
Byzantium (8 or 5)/10 (unknown effect)
Results if we convince Garp and Sigurd (guarantees the issue passes):
Asgard 14/10
Alfheim 4/10
Vanaheim 5/10
Jotunheim 6/10
Midgard 8/10
Svartalfheim 4/10
Niflheim 8/10
Muspelheim 11/10
Byzantium (8 or 4)/10 (unknown effect)
Either way this is something we can afford to do. Nobody's relations with us will become dangerously low (Vanaheim became lower than this during the got caught spying debacle), and with the expanded embassies we have a small but not insignificant chance of getting +1 to our relations each year (or is it turn?
@Durin - the option said year, but are you going to roll five times for each polity every turn or did you mean every year?) and that can get everyone back up to 10. If we need to we can also do some Relations actions, which get +10 due to the embassies.
The entire reason we build up these relations modifiers is so that we can spend them when we need to. This seems like one of those times to me.
At least some of the people voting in this quest do not agree with pursuing further relations with the Sirens. Please do not put it down to just game mechanics. I personally will find it distasteful to continue with this quest if the Trust resorts to such a heinous policy in the name of power. In my mind, sacrificing sapient souls to gain power puts those involved on the exact same level of Chaos.
The souls in question are already pretty much fucked no matter what happens. They are Chaos worshipers. Their souls belong to Chaos. That means that when we kill them their souls are absorbed by the Chaos God, empowering them and subjecting them to whatever fates those entities decide on. Well, with the exception of those who have enough favor that the Chaos Gods will bring them back, and if someone has that much favor then killing them isn't going to end them.
If the Sirens eat them, then their souls are digested and have all traces of what they once were removed, and the Chaos Gods don't get anything out of it. Whether the soul is destroyed or not wasn't stated in our research on the subject, but all Chaotic corruption is certainly removed either way.