User blog comment:FairyRaven/Fairy Tail Chapter 325: Unity, Review and Commentary/@comment-49.176.6.51-20130329100223/@comment-7418318-20130329104422

I'm not so sure about that. After all the dragon slayers did turn on their allies at some point, so I could imagine that many of the former pro-Human dragons might have switched sides. That is, if those old factions even held true anymore after Ancalogia became the kind of all dragons.

What I am sure about is that Grandeene (however she's spelled...), Igneel and Metallicana wouldn't attack mandkind. After all why would they bother teaching Gajeel, Natsu and Wendy dragon slayer magic, if they intended to fight them later?