Hope was an idiot to do that, but Elijah not having memories is not an excuse. He lost his memories not his compassion, morality and knowledge of right and wrong. He chose to help the Purist, even when the actual family member and his fiance - Antoinette - was against them. He chose to stop Klaus from saving her. Just because he didn't remember her, doesn't mean it wasn't him. It's still partially his fault. Along with Hope, Greta and Roman.