Easy: If an enemy came, ready to destroy the grid, Quorra would - or at least, should - be ready to defend it with force.

Mercury is no longer the bridge-builder and diplomat she once was, it's true. But that prepared her for what she'd face, from beings from another dimension bent on using humans as nothing but their host bodies, to the incarnations of nightmares and death. There was no peaceful solution.

There was destruction, or battle.

"If you're not ready for that, you'll lose what you want to still have."