The "Preferred Xenotype" setting in Ideology makes your pawns have automatic -30 opinion of people of non-preferred xenotypes, making them rivals. This applies to raiders and random crash-landed people, so raids can give a mood bonus to racist pawns that hate everybody different from themselves

Noticed this today -- running a colony with a preference for a custom xenotype and there was a +3 mood bonus across the board after they killed a Yttakin raider. The "rival died" mood bonus stacks up to five times (according to the wiki) so I imagine at mid-late game you can get a relatively reliable +15 mood bonus, maybe more if the xenotypes are ugly (Wasters) or they just have one of the -opinion traits.

The calculations here rely on the idea that the actual magnitude of "rival died" mood bonus depends on the actual opinions between the pawns -- every -10 opinion confers a +1 mood. Please correct me if it does not actually work like that.

So if you capture Waster raiders (-30 for non-preferred xenotype, -20 for unattractive gene), I imagine you can disfigure them by tearing out their jaw or cutting out an eye (-15) then kill them, which should give you a +6 mood bonus for every dead Waster. If your guys are intensely bigoted, that adds an additional -25 opinion penalty, so the mood bonus goes up to +8. If they are staggeringly ugly, breathe creepily or have an annoying voice, then you can probably get the +10 bonus, but that does not seem very likely. But basically if you are fighting regular raiders, then you can get a +15 mood bonus after a raid. +25 for Wasters, +30 for processed Wasters, +40 for processed Wasters in a bigoted colony, and +50 if the stars align.