User blog comment:IamJakuhoRaikoben/Chapter 449: Mavis & Zeref, Review./@comment-7418318-20150824075033/@comment-128.141.153.156-20150824152353

Maybe Law is actually (potentially) able to kill people, so casting it is the same as claiming the right to decide who lives and who dies (I know, technically any lethal spell fulfills that, but this one is directly connected to the user's mind and feelings). It's not the same as resurrecting people, but I'd say it's enough to make a God of Death angry.