Well, it makes sense that erasing someone's faith would be cheap.
The whole thing with hell (depending on the lore you follow) is that hell wants to get as much souls as possible for one reason or another. Killing a person doesn't necessarily mean they'll go to hell so the 50/50 odds (or 1/3 if you think purgatory or ghosts happen) makes killing someone cheap, but erasing their faith in god guarantees they go to hell basically so that's another point in the devil's favor.
It's basically a steal to erase faith for 1 point since that's a soul the devil gets.