User blog comment:IamJakuhoRaikoben/Chapter 389: The Twin Dragons vs. The King of Hades, Review./@comment-24467372-20140620101344/@comment-7418318-20140620110334

That Dragon Slayer magic is different from regular magic is already an established fact ever since the Edolas arc, so even if that is what Mard meant, it's nothing new.

But maybe it's a lot less complicated and Mard just thinks that this kind of magic should be for the Dragons only and it was an affront to give mere Humans - being less than insects - such power.