User blog comment:Nerdyanimegirl225/The 3 picks/@comment-24039250-20140515191124/@comment-7418318-20140515215434

That he gave advice to Fairy Tail doesn't necessarily mean he's being nice.

His goal was to create the perfect world for mages and Tartaros intends to wipe out all mages and even magic itself, leaving only curses. Those are polar opposite goals and that makes Tartaros Hades' enemy either way, no matter on which side of the good/evil spectrum he is now.