I'm not so bothered about Seamus being a serial killer, I love the midnight stalker, it's the fact he's a super-rapist who has found a way to remove women of even more agency by literally turning their bodies into mindless puppets. Sonnia's doing a similar thing, and it's just as horrible there, but at least she's not doing it because it makes her feel good.
I think saying everyone is evil is a stretch with Malifaux. I think there are a bunch of people that are morally compromised but generally are trying to make things better for their people (Zoiraida, Ironsides, Reva, Ophelia, Von Schill, Lady J).
I don't think you can give the Guild any leeway though. Nobody asked them to rule the world, they took it because they wanted the power that running it gave them. That's why they're institutionally corrupt, they're just power hungry at their core. I don't see them as hugely analogous to stuff in our world though, I like them as a faction, they're what'd happen if the illuminati went public.