I think what you're saying In the Onion scenario is that killing half of nonbelievers is basically just as bad as killing ALL nonbelievers, right? I agree.

So what that means is that we could still be precisely honest about the cleric's intentions without letting him off the hook at all. The honesty doesn't diminish our ability to condemn him in the slightest, because what he wants to do is STILL TERRIBLE.

But the honesty does strengthen our argument, because it is TRUE. And because it is TRUE, means it actually gives us more solid ground for condemning him than we have if we try to use the exaggeration, which is ultimately a type of FALSEHOOD.

This is my point. Don't use exaggeration when the honest truth is all you need. Exaggerations pollute our ability to understand what is actually taking place.