Because canon includes a certain character who feels lots and lots of pain, which Eragon is explicitly responsible for.

Yep. So Elva's just been storing up ammunition for the empathy spell without knowing or wanting to. Which is also horrible.

I don't think you're going to hit Eragon with the empathy spell, though. I think Eragon's going to use it against Vanora, and it's going to make her stronger instead of weaker.