If the men who would otherwise become slaves from the raiding are now going to be turned into women, raiding seems less than helpful for acquiring more slaves.
Okay, so take the narratives of each:
-Slaves
Their leading families will be picking dissidents, criminals and low status individuals to enslave and send as tribute. Over time this would actually reinforce their slavery practices as they would be compelled to keep enslaving their own people for tribute, while on our part, we'd be receiving former slaves with limited value skills who need retraining, overcome culture clash
and avoid becoming a de-facto underclass.
They also have a vested interest in retaining their female slaves, so you'd see a lot more male slaves, which would probably give our Fatherhood+Leader attribute a headache to see subservient men under Cath wives.
Its very easy for people to casually slide into making the ex-slaves do all the dirty and menial work, after all they're already used to the work and unlikely to complain. Which means in turn their children would not have as much opportunity to become farmers, hunters and craftsmen because their parents never had such skills.
On their side, it means we spur conflict. We'd be encouraging them to generate more slaves, whether by internal conflict, by entrapment or other means, because they NEED slaves. And the thing is that slavery needs very little incentive to continue.
-Wives
The biggest problem here is that we have an
excess of women. We don't want more! Taking wives both harms the Sangere population dynamics AND ours.
The resultant scarcity of women in their society would apply strong pressure to do three things:
-Take Seryn's blessing regardless of personal desires. Their family would force them to via social pressure.
-Remove competitors. If theres too many men, then you'd just have to make sure a lot of them are removed from the competition. Slavery is one outlet where less successful men can be eliminated from the pool, as is exploration, civil war or dangerous initiation rites.
-End the tribute, by blood if necessary.
Ergo, Wives would either accelerate the social changes Seryn is trying to push or set their society on fire. On our side? We'd be normalizing polygamy, which would impact us as Spirit of the Father, especially when our edict is for our worshippers who wish to become Cath to need to sire 2 children, so the optimal route is to have two wives, sire one child on both, then become Cath.
-Children
The biggest problem here is that most families would have difficulties giving up their children, which would impose some social strain down the line until they get used to the idea. Fortunately the current Sangere situation is that they're already devaluing a big chunk of their children due to child mortality and that they are already writing off their female children as non-persons, so we can wedge in giving up children for adoption as a social value during the transition.
However on a population dynamics level, this is a strong positive. The Sangere get to rebalance their population by giving us excess sons they can't afford to raise as warrior-farmers(this is the only way giving men to us is socially acceptable under their model other than as slaves). We get a steady influx of fresh blood to balance out the Cath monotyping.
Culturally it helps that the new population are children, which we get to culturally convert more easily than adults, and they also fill the gap between former-male-Cath unwilling to take a husband with adopted children until Seryn figures out the magic.
Finally, as Spirit of the Father, adopting children is resonant with our themes and helps expand the definition of Family.
).