User blog comment:FairyRaven/Fairy Tail Chapter 372: Breach, Review and Commentary/@comment-5598380-20140221101346/@comment-7418318-20140221103501

Zeref is trying to destroy mankind. If his words about the connection between the controll of his powers and his valuing Human life were true (and we have no indication of it not so), there won't be any accidential discharges.

And with that expression on Zeref's face, he doesn't look like he wants to kill Natsu.

That is, if that's Zeref and he's physically present in the first place.