My take on the role of the GM is this: I'm a fan of the characters, and I'm there to make live dangerous, exciting and heroic. So my job is to push the players to the limit and make them be awesome to survive. It's a fine line, and sometimes a character will fall over the edge, but if they die being awesome, then that's an awesome death.
I don't see myself as neutral, to me, that implies that I"m just applying the rules impassively. I don't. I pull blows, I foretell doom, and when the PCs know how deadly it is and have made the choice to stick it out, I'll pound them and see what falls out.
In my Living Dungeon World finale, the Ysolde the Archmage (L4 or 5 Wizard) was facing down an Avatar of Orcus, blasting it with fireball after fireball and absorbing attacks with his mirror image until they were all gone, then he threw his magical simalcra in the way of the crushing fist of the Avatar, and missed. "The fist drives into you for 30 points of damage", I said. I knew the blow would kill Ysolde When from the other side of the table, a hand is interposed, thrust between me and Ysolde's player, it's Regulus the Paladin (I think, level 3, just), "I have two Defence hold, I throw myself in front of the Avatar's fist, and half the damage".
DUNGEON WORLD!