That's a great idea, and one that seems so simple it's a wonder nobody has thought of it before.

However, keep in mind that healers do things that defenders do not, most notably uncurse. All those cursed items that villagers regularly obtain - even things like keys from the maus, let alone the various equ items - would no longer be uncursed. You'd have to somehow get a defender to learn that ability.

It's possible, mind you. There was a paladin villager, and paladins have the remove curse supplication. If you made that paladin a defender and allowed him to use that supplication, then you're ok.

But otherwise I think the benefit of having a cabal defender that can bandage you (i.e. a 150 hp heal) every other tick is not worth losing the only place in the game most villagers can get things uncursed. (I say most because those villagers who worship imms that have shrines, and in whose shrines there are healers, can get things uncursed there.)