User blog comment:Onic14/God Slayer Magic: Made to slay Zeref/@comment-5914413-20150403012352

Didn't Natsu gain dragon slayer magic because Igneel couldn't kill him and just decided to teach a demon he couldn't kill the magic to slay dragons?

Which also brings up the questions of why natsu didn't kill igneel back when he was still a demon, or why the damned dragon thought it would be a good idea to teach a demon made to kill zeref the magic to slay dragons to name just two of the questions that will spring from that first question.